Task: First perfect square in base n with n unique digits
C++: #include <string>
#include <iostream> 
#include <cstdlib>
#include <math.h>
#include <chrono>
#include <iomanip>

using namespace std;

const int maxBase = 16;  
int base, bmo, tc; 
const string chars = "0123456789ABCDEF"; 
unsigned long long full; 


string toStr(const unsigned long long ull) {
	unsigned long long u = ull; string res = ""; while (u > 0) {
		lldiv_t result1 = lldiv(u, base); res = chars[(int)result1.rem] + res;
		u = (unsigned long long)result1.quot;
	} return res;
}


unsigned long long to10(string s) {
	unsigned long long res = 0; for (char i : s) res = res * base + chars.find(i); return res;
}


bool allIn(const unsigned long long ull) {
	unsigned long long u, found; u = ull; found = 0; while (u > 0) {
		lldiv_t result1 = lldiv(u, base); found |= (unsigned long long)1 << result1.rem;
		u = result1.quot;
	} return found == full;
}


string fixup(int n) {
	string res = chars.substr(0, base); if (n > 0) res = res.insert(n, chars.substr(n, 1));
	return "10" + res.substr(2);
}


void doOne() {
	bmo = base - 1; tc = 0; unsigned long long sq, rt, dn, d;
	int id = 0, dr = (base & 1) == 1 ? base >> 1 : 0, inc = 1, sdr[maxBase] = { 0 };
	full = ((unsigned long long)1 << base) - 1;
	int rc = 0; for (int i = 0; i < bmo; i++) {
		sdr[i] = (i * i) % bmo; if (sdr[i] == dr) rc++; if (sdr[i] == 0) sdr[i] += bmo;
	}
	if (dr > 0) {
		id = base; for (int i = 1; i <= dr; i++)
			if (sdr[i] >= dr) if (id > sdr[i]) id = sdr[i]; id -= dr;
	}
	sq = to10(fixup(id)); rt = (unsigned long long)sqrt(sq) + 1; sq = rt * rt;
	dn = (rt << 1) + 1; d = 1; if (base > 3 && rc > 0) {
		while (sq % bmo != dr) { rt += 1; sq += dn; dn += 2; } 
		inc = bmo / rc; if (inc > 1) { dn += rt * (inc - 2) - 1; d = inc * inc; }
		dn += dn + d;
	} d <<= 1;
	do { if (allIn(sq)) break; sq += dn; dn += d; tc++; } while (true);
	rt += tc * inc;
	cout << setw(4) << base << setw(3) << inc << "  " << setw(2)
		<< (id > 0 ? chars.substr(id, 1) : " ") << setw(10) << toStr(rt) << "  "
		<< setw(20) << left << toStr(sq) << right << setw(12) << tc << endl;
}

int main() {
	cout << "base inc id      root  sqr                   test count" << endl;
	auto st = chrono::system_clock::now();
	for (base = 2; base <= maxBase; base++) doOne();
	chrono::duration<double> et = chrono::system_clock::now() - st;
	cout << "\nComputation time was " << et.count() * 1000 << " milliseconds" << endl;
	return 0;
}

VB: Imports System.Numerics

Module Program
    Dim base, bm1 As Byte, hs As New HashSet(Of Byte), st0 As DateTime
    Const chars As String = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz|"

    
    Function toStr(ByVal b As BigInteger) As String
        toStr = "" : Dim re As BigInteger : While b > 0
            b = BigInteger.DivRem(b, base, re) : toStr = chars(CByte(re)) & toStr : End While
    End Function

    
    Function allIn(ByVal b As BigInteger) As Boolean
        Dim re As BigInteger : hs.Clear() : While b > 0 : b = BigInteger.DivRem(b, base, re)
            hs.Add(CByte(re)) : End While : Return hs.Count = base
    End Function

    
    Function allInQ(ByVal b As BigInteger) As Boolean
        Dim re As BigInteger, c As Integer = 0 : hs.Clear() : While b > 0 : b = BigInteger.DivRem(b, base, re)
            hs.Add(CByte(re)) : c += 1 : If c <> hs.Count Then Return False
        End While : Return True
    End Function

    
    Function to10(s As String) As BigInteger
        to10 = 0 : For Each i As Char In s : to10 = to10 * base + chars.IndexOf(i) : Next
    End Function

    
    Function fixup(n As Integer) As String
        fixup = chars.Substring(0, base)
        If n > 0 Then fixup = fixup.Insert(n, n.ToString)
        fixup = "10" & fixup.Substring(2)
    End Function

    
    Function IntSqRoot(v As BigInteger) As BigInteger
        IntSqRoot = New BigInteger(Math.Sqrt(CDbl(v))) : Dim term As BigInteger
        Do : term = v / IntSqRoot : If BigInteger.Abs(term - IntSqRoot) < 2 Then Exit Do
            IntSqRoot = (IntSqRoot + term) / 2 : Loop Until False
    End Function

    
    Sub doOne()
        bm1 = base - 1 : Dim dr As Byte = 0 : If (base And 1) = 1 Then dr = base >> 1
        Dim id As Integer = 0, inc As Integer = 1, i As Long = 0, st As DateTime = DateTime.Now
        Dim sdr(bm1 - 1) As Byte, rc As Byte = 0 : For i = 0 To bm1 - 1 : sdr(i) = (i * i) Mod bm1
            rc += If(sdr(i) = dr, 1, 0) : sdr(i) += If(sdr(i) = 0, bm1, 0) : Next : i = 0
        If dr > 0 Then
            id = base : For i = 1 To dr : If sdr(i) >= dr Then If id > sdr(i) Then id = sdr(i)
            Next : id -= dr : i = 0 : End If
        Dim sq As BigInteger = to10(fixup(id)), rt As BigInteger = IntSqRoot(sq) + 0,
            dn As BigInteger = (rt << 1) + 1, d As BigInteger = 1
        sq = rt * rt : If base > 3 AndAlso rc > 0 Then
            While sq Mod bm1 <> dr : rt += 1 : sq += dn : dn += 2 : End While 
            inc = bm1 \ rc : If inc > 1 Then dn += rt * (inc - 2) - 1 : d = inc * inc
            dn += dn + d
        End If : d <<= 1 : If base > 5 AndAlso rc > 0 Then : Do : If allInQ(sq) Then Exit Do
                sq += dn : dn += d : i += 1 : Loop Until False : Else : Do : If allIn(sq) Then Exit Do
                sq += dn : dn += d : i += 1 : Loop Until False : End If : rt += i * inc
        Console.WriteLine("{0,3} {1,3} {2,2} {3,20} -> {4,-38} {5,10} {6,8:0.000}s   {7,8:0.000}s",
                          base, inc, If(id = 0, " ", id.ToString), toStr(rt), toStr(sq), i,
                          (DateTime.Now - st).TotalSeconds, (DateTime.Now - st0).TotalSeconds)
    End Sub

    Sub Main(args As String())
        st0 = DateTime.Now
        Console.WriteLine("base inc id                root    square" & _
            "                                 test count    time        total")
        For base = 2 To 28 : doOne() : Next
        Console.WriteLine("Elasped time was {0,8:0.00} minutes", (DateTime.Now - st0).TotalMinutes)
    End Sub
End Module