func isPrime(value: Int) -> Bool {
if value < 2 { return false }
for baseDivisor in [2, 3, 5, 7] {
if value % baseDivisor == 0 { return value == baseDivisor }
}
for divisor in TakeWhile({ $0 * $0 <= value }, Count(7, by: 30)) {
for offset in [0, 4, 6, 10, 12, 16, 22, 24] {
if value % (divisor + offset) == 0 { return false }
}
}
return true
}