A174666 a(n) = 2 * a(n-2) * a(n-1) with a(1)=1 and a(2)=3.

1, 3, 6, 36, 432, 31104, 26873856, 1671768834048, 89853749822987698176, 300429397152833661135077712592896, 53989415782483456907192461472369228929621535219515392

Offset: 1

Author

Giovanni Teofilatto, Mar 26 2010

Keywords

• nonn

Links

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

Crossrefs

Cf. A000045, A000071, A166470.

Programs

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

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 *)
nxt[{a_,b_}]:={b,2*a*b}; NestList[nxt,{1,3},10][[;;,1]] (* Harvey P. Dale, Apr 08 2023 *)

SageMath

[2^(fibonacci(n)-1)*3^fibonacci(n-1) for n in range(1,13)] # G. C. Greubel, Jul 30 2024

Formula

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

a(n) = A166470(n-1)/2. - Alois P. Heinz, Sep 16 2022

Extensions

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