cp's OEIS Frontend

A329609 Numbers k such that A156552(k) is a multiple of 3.

%I A329609 #20 Jan 17 2023 16:32:36
%S A329609 1,4,9,10,16,21,22,25,30,34,36,39,40,46,49,55,57,62,64,66,81,82,84,85,
%T A329609 87,88,90,91,94,100,102,105,111,115,118,120,121,129,133,134,136,138,
%U A329609 144,146,154,155,156,159,160,166,169,183,184,186,187,189,194,195,196,198,203,205,206,213,218,220,225,228,235,237,238,246
%N A329609 Numbers k such that A156552(k) is a multiple of 3.
%C A329609 Not a multiplicative semigroup. For example, although 10 and 21 are present, 210 is missing. Compare to A332820. - _Antti Karttunen_, Jan 17 2023
%H A329609 Antti Karttunen, <a href="/A329609/b329609.txt">Table of n, a(n) for n = 1..20000</a>
%o A329609 (PARI)
%o A329609 A156552(n) = {my(f = factor(n), p2 = 1, res = 0); for(i = 1, #f~, p = 1 << (primepi(f[i, 1]) - 1); res += (p * p2 * (2^(f[i, 2]) - 1)); p2 <<= f[i, 2]); res}; \\ From A156552
%o A329609 isA329609(n) = !(A156552(n)%3);
%Y A329609 Cf. A000290 (subsequence), A156552, A329603, A329604, A332812.
%Y A329609 Positions of zeros in A329903, of nonzeros in A341353, of ones in A353269 (characteristic function), A353418 (Dirichlet inverse of char.fun), A359836.
%Y A329609 Sequence A332449 sorted into ascending order.
%Y A329609 Cf. also A353303, A353304 and A332820.
%K A329609 nonn
%O A329609 1,2
%A A329609 _Antti Karttunen_, Nov 21 2019