シクシク素数列 (Crystal)

シクシク素数列	https://qiita.com/advent-calendar/2018/4949prime-series
Crystal	https://qiita.com/cielavenir/items/4c95fdf14b7a247e51e0
Kuin	https://qiita.com/cielavenir/items/60993a2b2885690a3a4a
Swift	https://qiita.com/cielavenir/items/db4c93532a53bfa33ac2
Kotlin	https://qiita.com/cielavenir/items/f3ccdd5ebf245aba417c
Pascal	https://qiita.com/cielavenir/items/4c962db6825d9a5eb511

4949.cr

#!/usr/bin/env crystal
def isqrt(n)
    return 0 if n<=0
    return 1 if n<4 # 1
    x,y=0,n
    while x!=y&&x+1!=y
        x,y=y,(n/y+y)/2
    end
    x
end

def isPrime(i)
    return false if i<2
    (2..isqrt(i)).each{|j|
        if i%j<1
            return false
        end
    }
    true
end

def is4949(i)
    return false if i<=0
    return true if i%10==4||i%10==9
    is4949(i/10)
end

n=gets.not_nil!.to_i
i=2
cnt=0
while cnt<n
    if is4949(i)&&isPrime(i)
        print i
        if cnt<n-1
            print ","
        else
            puts
        end
        cnt+=1
    end
    i+=1
end