Buggy python submission (verdict: Time Limit Exceeded):
import sys
from math import ceil as C, floor as F, sqrt, gcd as G
from collections import defaultdict as D, Counter as CNT
from functools import reduce as R
import heapq as HQ
from operator import mul

class Heap:
  def __init__(self, data, reverse=False):
    self.reverse = -1 if reverse else 1
    self.data = [self.reverse * d for d in data]
    HQ.heapify(self.data)
  def push(self, x): return HQ.heappush(self.data, self.reverse * x)
  def pop(self): return self.reverse * HQ.heappop(self.data) 

ALP = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
alp = 'abcdefghijklmnopqrstuvwxyz'
def prod(list): return R(mul, list, 1)
def _X(): return sys.stdin.readline().rstrip().split(' ')
def _S(ss): return tuple(ss) if len(ss) > 1 else ss[0]
def S(): return _S(_X())
def Ss(): return list(S())
def _I(ss): return tuple([int(s) for s in ss]) if isinstance(ss, tuple) else int(ss)
def I(): return _I(S())
def _Is(ss): return list(ss) if isinstance(ss, tuple) else [ss]
def Is(): return _Is(I())

n = I()
rgb = S()

cnt = CNT(list(rgb))
ans = prod([cnt[c] for c in ['R', 'G', 'B']])

for i, r in enumerate(rgb):
    for j, g in enumerate(rgb[i+1:], start=i+1):
        k = j + (j - i)
        if k < len(rgb):
            if r != g and g != rgb[k] and r != rgb[k]:
                ans -= 1

print(ans)
        


Fixed submission:
import sys
from math import ceil as C, floor as F, sqrt, gcd as G
from collections import defaultdict as D, Counter as CNT
from functools import reduce as R
import heapq as HQ
from operator import mul

class Heap:
  def __init__(self, data, reverse=False):
    self.reverse = -1 if reverse else 1
    self.data = [self.reverse * d for d in data]
    HQ.heapify(self.data)
  def push(self, x): return HQ.heappush(self.data, self.reverse * x)
  def pop(self): return self.reverse * HQ.heappop(self.data) 

ALP = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
alp = 'abcdefghijklmnopqrstuvwxyz'
def prod(list): return R(mul, list, 1)
def _X(): return sys.stdin.readline().rstrip().split(' ')
def _S(ss): return tuple(ss) if len(ss) > 1 else ss[0]
def S(): return _S(_X())
def Ss(): return list(S())
def _I(ss): return tuple([int(s) for s in ss]) if isinstance(ss, tuple) else int(ss)
def I(): return _I(S())
def _Is(ss): return list(ss) if isinstance(ss, tuple) else [ss]
def Is(): return _Is(I())

n = I()
rgb = S()

cnt = CNT(list(rgb))
ans = prod([cnt[c] for c in ['R', 'G', 'B']])

for i, r in enumerate(rgb):
    for j, g in enumerate(rgb[i+1:], start=i+1):
        k = j + (j - i)
        if k < len(rgb):
            if r != g and g != rgb[k] and r != rgb[k]:
                ans -= 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
from math import ceil as C, floor as F, gcd as G, sqrt
from collections import defaultdict as D, Counter as CNT
from functools import reduce as R
import heapq as HQ

class Heap:
  def __init__(self, data, reverse=False):
    self.reverse = -1 if reverse else 1
    self.data = [self.reverse * d for d in data]
    HQ.heapify(self.data)
  def push(self, x): return HQ.heappush(self.data, self.reverse * x)
  def pop(self): return self.reverse * HQ.heappop(self.data)

  
ALP = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
alp = 'abcdefghijklmnopqrstuvwxyz'
def _X(): return sys.stdin.readline().rstrip().split(' ')
def _S(ss): return tuple(ss) if len(ss) > 1 else ss[0]
def S(): return _S(_X())
def Ss(): return list(S())
def _I(ss): return tuple([int(s) for s in ss]) if isinstance(ss, tuple) else int(ss)
def I(): return _I(S())
def _Is(ss): return list(ss) if isinstance(ss, tuple) else [ss]
def Is(): return _Is(I())

_ = I()
xs = list(S())

rs, gs, bs = [], [], []
for i, x in enumerate(xs, 1):
    if x == 'R':
        rs.append(i)
    if x == 'G':
        gs.append(i)
    if x == 'B':
        bs.append(i)

ans = 0
seen = D(lambda: False)
s = sorted([rs, gs, bs], key=lambda x: len(x))
for a in s[0]:
    for b in s[1]:
        ans += len(s[2])

        if a < b:
            i, j = a, b
        else:
            j, i = a, b

        if i - (j-i) in s[2]:
            if not seen[(i - (j-i), i, j)]:
                ans -= 1
                seen[(i - (j-i), i, j)] = True
        if j + (j-i) in s[2]:
            if not seen[(i, j, j+(j-i))]:
                ans -= 1
                seen[(i, j, j+(j-i))] = True
        if (i+j)/2 in s[2]:
            if not seen[(i, (i+j)/2, j)]:
                ans -= 1
                seen[(i, (i+j)/2, j)] = True

print(ans)

Fixed submission:
import sys
from math import ceil as C, floor as F, sqrt, gcd as G
from collections import defaultdict as D, Counter as CNT
from functools import reduce as R
import heapq as HQ
from operator import mul

class Heap:
  def __init__(self, data, reverse=False):
    self.reverse = -1 if reverse else 1
    self.data = [self.reverse * d for d in data]
    HQ.heapify(self.data)
  def push(self, x): return HQ.heappush(self.data, self.reverse * x)
  def pop(self): return self.reverse * HQ.heappop(self.data) 

ALP = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
alp = 'abcdefghijklmnopqrstuvwxyz'
def prod(list): return R(mul, list, 1)
def _X(): return sys.stdin.readline().rstrip().split(' ')
def _S(ss): return tuple(ss) if len(ss) > 1 else ss[0]
def S(): return _S(_X())
def Ss(): return list(S())
def _I(ss): return tuple([int(s) for s in ss]) if isinstance(ss, tuple) else int(ss)
def I(): return _I(S())
def _Is(ss): return list(ss) if isinstance(ss, tuple) else [ss]
def Is(): return _Is(I())

n = I()
rgb = S()

cnt = CNT(list(rgb))
ans = prod([cnt[c] for c in ['R', 'G', 'B']])

for i, r in enumerate(rgb):
    for j, g in enumerate(rgb[i+1:], start=i+1):
        k = j + (j - i)
        if k < len(rgb):
            if r != g and g != rgb[k] and r != rgb[k]:
                ans -= 1

print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
import numpy as np
from math import ceil as C, floor as F, sqrt
from collections import defaultdict as D, Counter as CNT
from functools import reduce as R
import heapq as HQ

class Heap:
  def __init__(self, data, reverse=False):
    self.reverse = -1 if reverse else 1
    self.data = [self.reverse * d for d in data]
    HQ.heapify(self.data)
  def push(self, x): return HQ.heappush(self.data, self.reverse * x)
  def pop(self): return self.reverse * HQ.heappop(self.data)

ALP = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
alp = 'abcdefghijklmnopqrstuvwxyz'
def _X(): return sys.stdin.readline().rstrip().split(' ')
def _S(ss): return tuple(ss) if len(ss) > 1 else ss[0]
def S(): return _S(_X())
def Ss(): return list(S())
def _I(ss): return tuple([int(s) for s in ss]) if isinstance(ss, tuple) else int(ss)
def I(): return _I(S())
def _Is(ss): return list(ss) if isinstance(ss, tuple) else [ss]
def Is(): return _Is(I())

_ = I()
xs = list(S())


rs, gs, bs = [], [], []
for i, x in enumerate(xs, 1):
    if x == 'R':
        rs.append(i)
    if x == 'G':
        gs.append(i)
    if x == 'B':
        bs.append(i)

ans = 0
seen = D(lambda: False)
s = sorted([rs, gs, bs], key=lambda x: len(x))
for a in s[0]:
    for b in s[1]:
        ans += len(s[2])

        if a < b:
            i, j = a, b
        else:
            j, i = a, b

        if i - (j-i) in s[2]:
            if not seen[(i - (j-i), i, j)]:
                ans -= 1
                seen[(i - (j-i), i, j)] = True
        if j + (j-i) in s[2]:
            if not seen[(i, j, j+(j-i))]:
                ans -= 1
                seen[(i, j, j+(j-i))] = True
        if (i+j)/2 in s[2]:
            if not seen[(i, (i+j)/2, j)]:
                ans -= 1
                seen[(i, (i+j)/2, j)] = True

print(ans)

Fixed submission:
import sys
from math import ceil as C, floor as F, sqrt, gcd as G
from collections import defaultdict as D, Counter as CNT
from functools import reduce as R
import heapq as HQ
from operator import mul

class Heap:
  def __init__(self, data, reverse=False):
    self.reverse = -1 if reverse else 1
    self.data = [self.reverse * d for d in data]
    HQ.heapify(self.data)
  def push(self, x): return HQ.heappush(self.data, self.reverse * x)
  def pop(self): return self.reverse * HQ.heappop(self.data) 

ALP = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
alp = 'abcdefghijklmnopqrstuvwxyz'
def prod(list): return R(mul, list, 1)
def _X(): return sys.stdin.readline().rstrip().split(' ')
def _S(ss): return tuple(ss) if len(ss) > 1 else ss[0]
def S(): return _S(_X())
def Ss(): return list(S())
def _I(ss): return tuple([int(s) for s in ss]) if isinstance(ss, tuple) else int(ss)
def I(): return _I(S())
def _Is(ss): return list(ss) if isinstance(ss, tuple) else [ss]
def Is(): return _Is(I())

n = I()
rgb = S()

cnt = CNT(list(rgb))
ans = prod([cnt[c] for c in ['R', 'G', 'B']])

for i, r in enumerate(rgb):
    for j, g in enumerate(rgb[i+1:], start=i+1):
        k = j + (j - i)
        if k < len(rgb):
            if r != g and g != rgb[k] and r != rgb[k]:
                ans -= 1

print(ans)