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A340993 a(n) is the (2n)-th term of the n-fold self-convolution of the sum of divisors function sigma. 2
1, 3, 17, 120, 885, 6713, 51932, 407214, 3224845, 25733325, 206584437, 1666561042, 13498994796, 109713432390, 894291885000, 7307812510970, 59847327807597, 491062976039618, 4036174402666925, 33224883837921930, 273873806179142545, 2260338391869532332 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..1080

FORMULA

a(n) = [x^(2n)] (Sum_{j>=1} sigma(j)*x^j)^n.

a(n) = A319083(2n,n).

MAPLE

b:= proc(n, k) option remember; `if`(k=0, 1,

      `if`(k=1, numtheory[sigma](n+1), (q->

       add(b(j, q)*b(n-j, k-q), j=0..n))(iquo(k, 2))))

    end:

a:= n-> b(n$2):

seq(a(n), n=0..23);

CROSSREFS

Cf. A000203, A319083.

Sequence in context: A074544 A165976 A121572 * A249924 A305307 A074543

Adjacent sequences:  A340990 A340991 A340992 * A340994 A340995 A340996

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Feb 01 2021

STATUS

approved

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Last modified April 16 07:59 EDT 2021. Contains 343030 sequences. (Running on oeis4.)