23, that's the 1st and 2nd prime numbers 2,3, put together side by side 35, that's the 2nd and 3rd prime numbers 3,5, put together side by side 57, that's the 3rd and 4th prime numbers 5,7 put together side by side 711, that's the 4th and 5th prime numbers 7,11 put together side by side 1113, that's the 5th and 6th prime numbers 11,13 put together side by side "solve these sum" <-- that makes no sense, sorry. Edwin