Consider a sequence made up of the consecutive prime numbers. This infinite sequence would start with: 
```python
"2357111317192329313741434753596167717379..."
```
You will be given two numbers: `a` and `b`, and your task will be to return `b` elements starting from index `a` in this sequence.
```
For example:
solve(10,5) == `19232` Because these are 5 elements from index 10 in the sequence.
```
Tests go up to about index `20000`.
More examples in test cases. Good luck!
Please also try [Simple time difference](https://www.codewars.com/kata/5b76a34ff71e5de9db0000f2)
# pregenerate primes
LIMIT = 10**6
primes = []
sieve = list(range(LIMIT))
sieve[1] = 0
for n in sieve:
    if n:
        primes.append(n)
        for i in range(n*n, LIMIT, n): sieve[i] = 0

Copeland_Erdos = ''.join(map(str, primes))

def solve(a, b):
    return Copeland_Erdos[a:a+b]
# pregenerate primes
LIMIT = 10**6
primes = []
sieve = list(range(LIMIT))
sieve[1] = 0
for n in sieve:
    if n:
        primes.append(n)
        for i in range(n*n, LIMIT, n): sieve[i] = 0

Copeland_Erdos = ''.join(map(str, primes))

def solve(a, b):
    return Copeland_Erdos[a:a+b]