A184121 A (4,-3) Somos-4 sequence.

1, -1, -7, -31, -23, 2239, 39889, 603521, -27466831, -2445382081, -204734091383, 7545563759329, 7265319037194073, 2502938339020429439, 404477135616551491361, -932929530161758614571519

Offset

0,3

Comments

Hankel transform of A184120.

Links

G. C. Greubel, Table of n, a(n) for n = 0..75

Formula

a(n) = (4*a(n-1)*a(n-3) - 3*a(n-2)^2)/a(n-4).

Mathematica

RecurrenceTable[{a[0]==1, a[1]==-1, a[2]==-7, a[3]==-31, a[n]==(4a[n-1] a[n-3]- 3a[n-2]^2)/a[n-4]}, a, {n, 20}] (* Harvey P. Dale, Apr 03 2016 *)

Prog

(Magma) I:=[-23, 2239, 39889, 603521]; [1, -1, -7, -31] cat [n le 4 select I[n] else (4*Self(n-1)*Self(n-3) - 3*Self(n-2)^2 )/Self(n-4): n in [1..30]]; // G. C. Greubel, Aug 14 2018

Crossrefs

Sequence in context: A221402 A065916 A122654 * A167768 A103630 A205711

Adjacent sequences: A184118 A184119 A184120 * A184122 A184123 A184124

Keyword

sign,easy

Author

Paul Barry, Jan 09 2011

Status

approved