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A307306 Self-composition of the sum of divisors function (A000203). 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified June 6 11:14 EDT 2020. Contains 334827 sequences. (Running on oeis4.)