A111288 a(1) = a(2) = a(3) = a(4) = 1. For n>= 5, a(n) = a(n-1)*a(n-3) + a(n-2)*a(n-4).

1, 1, 1, 1, 2, 3, 5, 13, 49, 284, 3937, 196605, 56028733, 220640957641, 43379336062130626, 2430489281321503732285663, 536265482569392926735606762349877841, 23262840586898349755381222452865322555989091379459449

Offset

1,5

Links

Michael De Vlieger, Table of n, a(n) for n = 1..25

Mathematica

{1, 1, 1}~Join~NestList[{#2, #3, #4, #4 #2 + #3 #1} & @@ # &, {1, 1, 1, 1}, 14][[All, -1]] (* Michael De Vlieger, Sep 28 2017 *)

Prog

(PARI) a(n)=if(n<5, 1, a(n-1)*a(n-3) + a(n-2)*a(n-4)) \\ Lambert Klasen
(Magma) I:=[1, 1, 1, 1, 2]; [n le 4 select I[n] else Self(n-1)*Self(n-3)+Self(n-2)*Self(n-4) : n in [1..20]]; // Vincenzo Librandi, Sep 29 2017

Crossrefs

Sequence in context: A377808 A215102 A110364 * A064526 A261192 A103594

Adjacent sequences: A111285 A111286 A111287 * A111289 A111290 A111291

Keyword

easy,nonn

Author

Leroy Quet, Nov 01 2005

Extensions

More terms from Lambert Klasen (lambert.klasen(AT)gmx.net), Nov 06 2005

Status

approved