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A307305 Self-composition of the number of divisors function (A000005). 2
1, 4, 12, 34, 92, 246, 640, 1660, 4264, 10914, 27732, 70247, 177466, 447570, 1126344, 2828465, 7089391, 17746456, 44384884, 110927184, 276993616, 691007612, 1722214602, 4289021667, 10675557184, 26561494820, 66063726382, 164248795485, 408168287028, 1013819012498 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 1..760

Eric Weisstein's World of Mathematics, Divisor Function

FORMULA

G.f.: g(g(x)), where g(x) = Sum_{k>=1} x^k/(1 - x^k) is the g.f. of A000005.

MATHEMATICA

g[x_] := g[x] = Sum[x^k/(1 - x^k), {k, 1, 30}]; a[n_] := a[n] = SeriesCoefficient[g[g[x]], {x, 0, n}]; Table[a[n], {n, 30}]

CROSSREFS

Cf. A000005, A010553, A055507, A307306.

Sequence in context: A191823 A110335 A166294 * A176753 A248873 A180224

Adjacent sequences:  A307302 A307303 A307304 * A307306 A307307 A307308

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, Apr 01 2019

STATUS

approved

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Last modified February 17 12:29 EST 2020. Contains 331996 sequences. (Running on oeis4.)