A111288 - OEIS

%I #13 Sep 08 2022 08:45:21

%S 1,1,1,1,2,3,5,13,49,284,3937,196605,56028733,220640957641,

%T 43379336062130626,2430489281321503732285663,

%U 536265482569392926735606762349877841,23262840586898349755381222452865322555989091379459449

%N 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).

%H Michael De Vlieger, <a href="/A111288/b111288.txt">Table of n, a(n) for n = 1..25</a>

%t {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 *)

%o (PARI) a(n)=if(n<5,1,a(n-1)*a(n-3) + a(n-2)*a(n-4)) \\ Lambert Klasen

%o (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

%K easy,nonn

%O 1,5

%A _Leroy Quet_, Nov 01 2005

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