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A320225 a(1) = 1; a(n > 1) = Sum_{k = 1...n} Sum_{d|k, d < k} a(d). 5
1, 1, 2, 4, 5, 9, 10, 16, 19, 26, 27, 44, 45, 57, 65, 87, 88, 120, 121, 158, 171, 200, 201, 278, 284, 331, 353, 426, 427, 536, 537, 646, 676, 766, 782, 982, 983, 1106, 1154, 1365, 1366, 1617, 1618, 1851, 1943, 2146, 2147, 2589, 2600, 2917, 3008, 3390, 3391 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Seiichi Manyama, Table of n, a(n) for n = 1..10000

FORMULA

a(1) = 1; a(n > 1) = Sum_{d = 1...n-1} a(d) * floor(n/d-1).

G.f. A(x) satisfies A(x) = x + (1/(1 - x)) * Sum_{k>=2} A(x^k). - Ilya Gutkovskiy, Sep 06 2019

MATHEMATICA

sau[n_]:=If[n==1, 1, Sum[sau[d], {k, n}, {d, Most[Divisors[k]]}]];

Table[sau[n], {n, 30}]

CROSSREFS

Cf. A002541, A003238, A010766, A014668, A126656, A167865, A316782, A317712, A320222, A320224.

Sequence in context: A280729 A213011 A175265 * A070924 A266197 A086638

Adjacent sequences:  A320222 A320223 A320224 * A320226 A320227 A320228

KEYWORD

nonn

AUTHOR

Gus Wiseman, Oct 07 2018

STATUS

approved

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Last modified May 30 17:32 EDT 2020. Contains 334728 sequences. (Running on oeis4.)