Warning: With enough thinking anyone can come up with a solution without knowing any specific algorithm.

that was nice

Average java enjoyer

Way too easy for 5kyu

A little tip, you could start from 3 and go i+=2 in isPrime, (checking before is the num passed is two)

There's a pattern indeed but I can't figure it out

I can't either after spending all day with 3 different algorithms...

That's not true, my solution in java uses 2 loops

Very nice kata :)

Didn't know about those substring methods

Too easy for 6kyu

That's my solution but with less code and more readable :

Nice kata as always :)

Lo dejé de intentar hace meses, pero le daré otro intento a ver que tal :)

Very good kata. :D