Task: First perfect square in base n with n unique digits
Go: package main

import (
    "fmt"
    "math/big"
    "strconv"
    "time"
)

const maxBase = 27
const minSq36 = "1023456789abcdefghijklmnopqrstuvwxyz"
const minSq36x = "10123456789abcdefghijklmnopqrstuvwxyz"

var bigZero = new(big.Int)
var bigOne = new(big.Int).SetUint64(1)

func containsAll(sq string, base int) bool {
    var found [maxBase]byte
    le := len(sq)
    reps := 0
    for _, r := range sq {
        d := r - 48
        if d > 38 {
            d -= 39
        }
        found[d]++
        if found[d] > 1 {
            reps++
            if le-reps < base {
                return false
            }
        }
    }
    return true
}

func sumDigits(n, base *big.Int) *big.Int {
    q := new(big.Int).Set(n)
    r := new(big.Int)
    sum := new(big.Int).Set(bigZero)
    for q.Cmp(bigZero) == 1 {
        q.QuoRem(q, base, r)
        sum.Add(sum, r)
    }
    return sum
}

func digitalRoot(n *big.Int, base int) int {
    root := new(big.Int)
    b := big.NewInt(int64(base))
    for i := new(big.Int).Set(n); i.Cmp(b) >= 0; i.Set(root) {
        root.Set(sumDigits(i, b))
    }
    return int(root.Int64())
}

func minStart(base int) (string, uint64, int) {
    nn := new(big.Int)
    ms := minSq36[:base]
    nn.SetString(ms, base)
    bdr := digitalRoot(nn, base)
    var drs []int
    var ixs []uint64
    for n := uint64(1); n < uint64(2*base); n++ {
        nn.SetUint64(n * n)
        dr := digitalRoot(nn, base)
        if dr == 0 {
            dr = int(n * n)
        }
        if dr == bdr {
            ixs = append(ixs, n)
        }
        if n < uint64(base) && dr >= bdr {
            drs = append(drs, dr)
        }
    }
    inc := uint64(1)
    if len(ixs) >= 2 && base != 3 {
        inc = ixs[1] - ixs[0]
    }
    if len(drs) == 0 {
        return ms, inc, bdr
    }
    min := drs[0]
    for _, dr := range drs[1:] {
        if dr < min {
            min = dr
        }
    }
    rd := min - bdr
    if rd == 0 {
        return ms, inc, bdr
    }
    if rd == 1 {
        return minSq36x[:base+1], 1, bdr
    }
    ins := string(minSq36[rd])
    return (minSq36[:rd] + ins + minSq36[rd:])[:base+1], inc, bdr
}

func main() {
    start := time.Now()
    var nb, nn big.Int
    for n, k, base := uint64(2), uint64(1), 2; ; n += k {
        if base > 2 && n%uint64(base) == 0 {
            continue
        } 
        nb.SetUint64(n)
        sq := nb.Mul(&nb, &nb).Text(base)
        if !containsAll(sq, base) {
            continue
        }
        ns := strconv.FormatUint(n, base)
        tt := time.Since(start).Seconds()
        fmt.Printf("Base %2d:%15s² = %-27s in %8.3fs\n", base, ns, sq, tt)
        if base == maxBase {
            break
        }
        base++
        ms, inc, bdr := minStart(base)
        k = inc
        nn.SetString(ms, base)
        nb.Sqrt(&nn)
        if nb.Uint64() < n+1 {
            nb.SetUint64(n + 1)
        }
        if k != 1 {
            for {
                nn.Mul(&nb, &nb)
                dr := digitalRoot(&nn, base)
                if dr == bdr {
                    n = nb.Uint64() - k
                    break
                }
                nb.Add(&nb, bigOne)
            }
        } else {
            n = nb.Uint64() - k
        }
    }
}

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