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A217628
a(n) = 3^((n-1)*(n+2)/2).
2
1, 9, 243, 19683, 4782969, 3486784401, 7625597484987, 50031545098999707, 984770902183611232881, 58149737003040059690390169, 10301051460877537453973547267843, 5474401089420219382077155933569751763, 8727963568087712425891397479476727340041449
OFFSET
1,2
LINKS
FORMULA
a(1) = 1, a(n) = a(n-1) * 3^n.
G.f.: G(0)/(2*x^3) - 1/(3*x)- 1/(3*x^2)- 1/(2*x^3), where G(k)= 1 + 3^(k-1)*x/(1 - 1/(1 + 1/G(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Jul 28 2013
MATHEMATICA
Table[3^((n-1) * (n+2)/2), {n, 1, 30}]
PROG
(Magma) I:=[1]; [n le 1 select I[n] else Self(n-1)*3^n: n in [1..20]]
(Maxima) A217628[n]:=3^((n-1)*(n+2)/2)$
makelist(A217628[n], n, 1, 30); /* Martin Ettl, Oct 29 2012 */
CROSSREFS
Cf. A036442.
Sequence in context: A013733 A369533 A295228 * A167005 A112028 A375178
KEYWORD
nonn
AUTHOR
Vincenzo Librandi, Oct 24 2012
STATUS
approved