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

1,2

Links

Vaclav Kotesovec, Table of n, a(n) for n = 1..750

Eric Weisstein's World of Mathematics, Divisor Function

Formula

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

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}]

Crossrefs

Cf. A000203, A000385, A051027, A307305.

Sequence in context: A301476 A290347 A034560 * A143955 A256428 A196860

Adjacent sequences: A307303 A307304 A307305 * A307307 A307308 A307309

Keyword

nonn

Author

Ilya Gutkovskiy, Apr 01 2019

Status

approved