A202238 Characteristic function of positive integers not prime and not a power of 2.

0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1

Offset: 1

Author

Michael Somos, Dec 16 2011

Keywords

• nonn
• easy

Links

• Antti Karttunen, Table of n, a(n) for n = 1..65537
• Index entries for characteristic functions

Crossrefs

Cf. A010051, A111774, A111775, A111787, A209229.

Programs

PARI

{a(n) = n>0 && !isprime(n) && n != 2^valuation(n, 2)}

Python

from sympy import isprime
def A202238(n): return int(not isprime(n) and bool((n&-n)^n)) # Chai Wah Wu, Mar 11 2025

Formula

A111775(n) = 0 if and only if a(n) = 0.

A111787(n) = 0 if and only if a(n) = 0.

a(n) = 1 for n in A111774. - Michel Marcus, Aug 28 2017