A015489 a(0)=1, a(1)=4, a(n) = sum_{k=0}^{k=n-1} 4^k a(k).

1, 4, 17, 289, 18785, 4827745, 4948438625, 20273753046625, 332185443668950625, 21770437421732017110625, 5707011317919939625464790625, 5984240806710536532650993759190625

Offset

0,2

Links

Table of n, a(n) for n=0..11.

Formula

a(n) = (4^(n-2) + 1) * a(n-1). - Vincenzo Librandi, Nov 11 2012

Prog

(Magma) I:=[1, 4, 17]; [n le 3 select I[n] else (4^(n-2)+1)*Self(n-1): n in [1..15]]; // _Vincenzo Librandi, Nov 11 2012

Crossrefs

Sequence in context: A214143 A320986 A302145 * A153061 A277762 A337477

Adjacent sequences: A015486 A015487 A015488 * A015490 A015491 A015492

Keyword

nonn,easy

Author

Olivier Gérard

Status

approved