A351787 a(1) = 1; a(n+1) = a(n) + Sum_{d|n} a(n/d) * a(d).

1, 2, 6, 18, 58, 174, 546, 1638, 4986, 14994, 45214, 135642, 407838, 1223514, 3672726, 11018874, 33063498, 99190494, 297593514, 892780542, 2678403690, 8035217622, 24105833722, 72317501166, 216953071986, 650859219322, 1952579289318, 5857737927786, 17573218697070

Offset

1,2

Links

Table of n, a(n) for n=1..29.

Formula

G.f.: x * ( 1 + Sum_{i>=1} Sum_{j>=1} a(i) * a(j) * x^(i*j) ) / (1 - x).

Mathematica

a[1] = 1; a[n_] := a[n] = a[n - 1] + Sum[a[(n - 1)/d] a[d], {d, Divisors[n - 1]}]; Table[a[n], {n, 1, 29}]

Crossrefs

Cf. A038044, A084978, A122698, A277120, A339755, A341697, A345139, A351788.

Sequence in context: A148459 A324166 A355388 * A307755 A304200 A081057

Adjacent sequences: A351784 A351785 A351786 * A351788 A351789 A351790

Keyword

nonn

Author

Ilya Gutkovskiy, Feb 19 2022

Status

approved