OFFSET
1,3
COMMENTS
From Antti Karttunen, May 27 2024 and Jun 12 2024: (Start)
This is a multiplicative semigroup: if m and n are in the sequence then so is m*n, and is generated by A008591 and A369659.
Term is present if and only if it is either a multiple of 9, or it is not a multiple of 3 and the sum of its prime factors (with repetition, A001414) is a multiple of 3, which happens iff the multiplicities of prime factors of the form 3m+1 (A002476) and of the form 3m-1 (A003627) are equal modulo 3.
(End)
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10000
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Sep 30 2019
STATUS
approved