1,1

A subsequence of A008586.

Ivan N. Ianakiev, Table of n, a(n) for n = 1..10000

a(n) == 0 (mod 4)

A tetrahedral die whose faces are marked with the numbers from 1 to 4 has an even number of sides marked with prime numbers, even integers and odd integers. Therefore, 4 is in the sequence.

Cf. A008586, A237989.

Sequence in context: A181471 A272753 A272804 * A312807 A312808 A249486

Adjacent sequences: A237987 A237988 A237989 * A237991 A237992 A237993

nonn,easy

Ivan N. Ianakiev, Feb 16 2014

approved