A371640 a(n) = 3^(2*n + valuation(n, 3)) = 3^A371638(n).

9, 81, 2187, 6561, 59049, 1594323, 4782969, 43046721, 3486784401, 3486784401, 31381059609, 847288609443, 2541865828329, 22876792454961, 617673396283947, 1853020188851841, 16677181699666569, 1350851717672992089, 1350851717672992089, 12157665459056928801, 328256967394537077627

Offset: 1

Author

Peter Luschny, Mar 30 2024

Keywords

• nonn

Comments

See A371639 for the connection with Voronoi's congruence.

Crossrefs

Cf. A371638, A371639 (numerator Voronoi).

Programs

Maple

A371640 := n -> 3^(2*n + padic:-ordp(n, 3)):
seq(A371640(n), n = 1..21);

SageMath

def A371640(n): return 3**(2*n + valuation(n, 3))
print([A371640(n) for n in range(1, 22)])

Formula

a(n) = denominator(Voronoi(3, 2*n)) where Voronoi(c, n) = ((c^n - 1)*Bernoulli(n)) / (n*c^(n - 1)).