1,2

Also, odd numbers such that sigma(sigma(n)) is in A028982.

Subsequence of odd terms of A234639. See also A234638, and A234641 with further cross references.

Table of n, a(n) for n=1..52.

(PARI) forstep(n=1, 1999, 2, sigma(sigma(sigma(n)))%2 && print1(n", "))

Sequence in context: A303812 A259028 A317392 * A219258 A044861 A161835

Adjacent sequences: A234637 A234638 A234639 * A234641 A234642 A234643

nonn

M. F. Hasler, Dec 28 2013

approved