A393239 Numbers k such that A000219(k) == 0 (mod 3).

2, 3, 5, 6, 9, 12, 14, 15, 18, 21, 24, 25, 29, 33, 34, 36, 41, 42, 44, 45, 48, 51, 54, 57, 58, 60, 61, 62, 65, 67, 69, 70, 73, 74, 76, 78, 81, 83, 87, 88, 89, 90, 96, 101, 105, 106, 109, 110, 111, 112, 114, 117, 118, 119, 121, 123, 127, 128, 129, 132, 133, 135

Offset

1,1

Links

Table of n, a(n) for n=1..62.

Maple

b:= proc(n) option remember; `if`(n=0, 1, add(
      b(n-j)*numtheory[sigma][2](j), j=1..n)/n)
    end:
select(k-> irem(b(k), 3)=0, [$0..135])[];  # Alois P. Heinz, Feb 09 2026

Prog

(PARI)
A000219(N) = {my(q='q+O('q^(N+1))); Vec(1/prod(k=1, N, (1-q^k)^k))}
A393239(maxk) = {my(p = A000219(maxk), v = List()); for(i=1, maxk, if(p[i]%3==0, listput(v, i-1))); v}

Crossrefs

Cf. A000219, A040051, A380893.

Sequence in context: A186106 A329161 A124866 * A166247 A126785 A295586

Adjacent sequences: A393236 A393237 A393238 * A393240 A393241 A393242

Keyword

nonn

Author

John Tyler Rascoe, Feb 07 2026

Status

approved