A239967 a(n) = a(n-1)*a(n-2) - a(n-3)*a(n-4), starting with 1,1,2,2.

1, 1, 2, 2, 3, 4, 8, 26, 196, 5064, 992336, 5025184408, 4986671393704544, 25058943335463698842360448, 124960715887419957580506993886784668778624, 3131383498581835095655557937198087383978439131276209799741457913600

Offset

1,3

Links

Table of n, a(n) for n=1..16.

Prog

(PARI) al(n)=local(v=vector(n)); v[1]=v[2]=1; v[3]=v[4]=2; for(i=5, n, v[i]=v[i-1]*v[i-2]-v[i-3]*v[i-4]); v
(Magma) I:=[1, 1, 2, 2]; [n le 4 select I[n] else Self(n-1)*Self(n-2)-Self(n-3)*Self(n-4): n in [1..16]]; // Vincenzo Librandi, Mar 30 2014

Crossrefs

Cf. A111235.

Sequence in context: A153943 A361117 A049309 * A307891 A205118 A363745

Adjacent sequences: A239964 A239965 A239966 * A239968 A239969 A239970

Keyword

nonn

Author

Franklin T. Adams-Watters, Mar 29 2014

Status

approved