A307306 Self-composition of the sum of divisors function (A000203).

1, 6, 26, 101, 366, 1294, 4400, 14706, 48362, 157583, 507714, 1621211, 5138804, 16204008, 50867068, 159004142, 494928072, 1534638702, 4743180908, 14622202326, 44978845086, 138074363360, 422979847404, 1293101281551, 3945553307665, 12018461150832, 36556888102402

Offset: 1

Author

Ilya Gutkovskiy, Apr 01 2019

Keywords

• nonn

Links

• Vaclav Kotesovec, Table of n, a(n) for n = 1..750
• Eric Weisstein's World of Mathematics, Divisor Function

Crossrefs

Cf. A000203, A000385, A051027, A307305.

Programs

Mathematica

g[x_] := g[x] = Sum[k x^k/(1 - x^k), {k, 1, 27}]; a[n_] := a[n] = SeriesCoefficient[g[g[x]], {x, 0, n}]; Table[a[n], {n, 27}]

Formula

G.f.: g(g(x)), where g(x) = Sum_{k>=1} k*x^k/(1 - x^k) is the g.f. of A000203.