OFFSET
1,1
COMMENTS
Each term is either of the form A334092(n)*2^k, for some n >= 1, and k >= 0, or a product of two terms of A334101, whether distinct or not.
Binary weight (A000120) of these terms is always either 2, 3 or 4. It is 2 for those terms that are of the form 9*2^k, 4 for the terms of the form p*q*2^k, where p and q are two distinct Fermat primes (A019434), and 3 for the both terms of the form A334092(n)*2^k, and for the terms of the form (p^2)*(2^k), where p is a Fermat prime > 3.
PROG
(PARI)
A000265(n) = (n>>valuation(n, 2));
isA019434(n) = ((n>2)&&isprime(n)&&!bitand(n-2, n-1)); \\ Charfun for A019434, Fermat primes.
isA334102(n) = { n = A000265(n); if(isprime(n), isA019434(A000265(n-1)), if(bigomega(n)!=2, 0, factorback(apply(isA019434, factor(n)[, 1])))); };
(PARI)
isA334102(n) = (2==A329697(n));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Apr 14 2020
STATUS
approved