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A015502 a(1)=1, a(n) = Sum_{k=1..n-1} (3^k-1)/2 * a(k). 1
1, 1, 5, 70, 2870, 350140, 127801100, 139814403400, 458731057555400, 4514831068460246800, 133300387296288786770000, 11806948504381482999365980000, 3137354163532752044074527571580000, 2500979519710095684958538548015855960000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Table of n, a(n) for n=1..14.

FORMULA

a(n) = ((3^(n-1) + 1)/2) * a(n-1). - Vincenzo Librandi, Nov 11 2012

a(n) ~ c * 3^(n*(n-1)/2) / 2^(n+1), where c = A132323 = QPochhammer(-1, 1/3) = 3.129868... . - Vaclav Kotesovec, Mar 24 2017

MATHEMATICA

Flatten[{1, Table[QPochhammer[-1, 3, n]/2^(n+1), {n, 2, 15}]}] (* Vaclav Kotesovec, Mar 24 2017 *)

PROG

(MAGMA) I:=[1, 1, 5]; [n le 3 select I[n] else ((3^(n-1) + 1)/2) * Self(n-1): n in [1..15]]; // Vincenzo Librandi, Nov 11 2012

CROSSREFS

Cf. A156296.

Sequence in context: A302910 A174486 A135438 * A303291 A324229 A338989

Adjacent sequences:  A015499 A015500 A015501 * A015503 A015504 A015505

KEYWORD

nonn,easy

AUTHOR

Olivier Gérard

STATUS

approved

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Last modified October 21 01:05 EDT 2021. Contains 348120 sequences. (Running on oeis4.)