A353476 a(n) = 1 if n is a semiprime of the form p * q, where p and q are (not necessarily distinct) primes with p <= q < p^2, otherwise 0.

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

Offset

1

Links

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

Index entries for characteristic functions

Formula

a(n) = A064911(n) - A353475(n).

Prog

(PARI) A353476(n) = if(2==isprimepower(n), 1, my(f=factor(n)); if(#f~ != 2, 0, (1==f[1, 2] && 1==f[2, 2] && (f[2, 1]) < f[1, 1]^2)));

Crossrefs

Characteristic function of A251728.

Cf. A064911, A353475.

Sequence in context: A072783 A353478 A353555 * A288377 A341609 A064911

Adjacent sequences: A353473 A353474 A353475 * A353477 A353478 A353479

Keyword

nonn

Author

Antti Karttunen, Apr 22 2022

Status

approved