18986domain: NAppears in sequencesFibonacci sequence beginning 2, 18.at n=16A022371a(n) is twice the smallest k such that A051686(k) = prime(n).at n=31A051692Twice the positions in A051686 at which new primes appear in that sequence.at n=44A051861Sum of composite numbers up to n is palindromic.at n=11A057959