170420

Appears in sequences

• Number of 2-vexillary permutations in S_n, that, permutations whose Stanley symmetric function has at most 2 terms or at most 2 Edelman-Greene tableaux.at n=9A224318
• Numbers k for which k = phi(k') + phi(k''), where phi is the Euler totient function (A000010), k' the arithmetic derivative of k (A003415) and k'' the second arithmetic derivative of k (A068346).at n=36A352332