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A174666 a(n) = 2 * a(n-2) * a(n-1) with a(1)=1 and a(2)=3. 2
1, 3, 6, 36, 432, 31104, 26873856, 1671768834048, 89853749822987698176, 300429397152833661135077712592896, 53989415782483456907192461472369228929621535219515392 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..17

FORMULA

a(n) = 2^A000071(n)* 3^A000045(n-1). [R. J. Mathar, Mar 30 2010]

MATHEMATICA

Nest[Append[#, 2Times@@Take[#, -2]]&, {1, 3}, 10]  (* Harvey P. Dale, Apr 20 2011 *)

RecurrenceTable[{a[1] == 1, a[2] == 3, a[n] == 2 a[n-2] a[n-1]}, a, {n, 12}] (* Vincenzo Librandi, Jun 19 2016 *)

PROG

(MAGMA) I:=[1, 3]; [n le 2 select I[n] else 2*Self(n-2)*Self(n-1): n in [1..11]]; // Vincenzo Librandi, Jun 19 2016

CROSSREFS

Sequence in context: A048642 A264702 A077532 * A211893 A093800 A068776

Adjacent sequences:  A174663 A174664 A174665 * A174667 A174668 A174669

KEYWORD

nonn

AUTHOR

Giovanni Teofilatto, Mar 26 2010

EXTENSIONS

Formula replaced by a non-redundant one by R. J. Mathar, Mar 30 2010

STATUS

approved

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Last modified December 8 11:10 EST 2021. Contains 349594 sequences. (Running on oeis4.)