Hello Seq-Fans, Write down the prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, ... Insert between two primes the smallest integer not yet present in the sequence such that two neighboring integers sum up to a prime. I think the sequence starts: 2,0,3,8,5,6,7,12,11,18,13,26,17,... Best, É.