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

1,1

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for characteristic functions

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

Prog

(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

Crossrefs

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

Sequence in context: A169672 A011672 A353492 * A144194 A144196 A156659

Adjacent sequences: A202235 A202236 A202237 * A202239 A202240 A202241

Keyword

nonn,easy,changed

Author

Michael Somos, Dec 16 2011

Status

approved