A162546 A Somos-4 variant: a(n) = (36*a(n-1)*a(n-3) - 68*a(n-2)^2)/a(n-4).

1, 1, -16, -644, -40592, -4821056, 17059328, 2492895195136, 10659285907800064, 86296767700623425536, 1081586547380924161458176, -36649408809924048998874742784, -18144416387824430577315746611724288

Offset

0,3

Comments

Hankel transform of A162543, A162548.

Links

Fung Lam, Table of n, a(n) for n = 0..67

Mathematica

RecurrenceTable[{a[n]==(36*a[n-1]*a[n-3] - 68*a[n-2]^2)/a[n-4], a[0]==1, a[1]==1, a[2]==-16, a[3]==-644}, a, {n, 20}] (* G. C. Greubel, Feb 23 2019 *)

Prog

(PARI) m=20; v=concat([1, 1, -16, -644], vector(m-4)); for(n=5, m, v[n] = (36*v[n-1]*v[n-3] -68*v[n-2]^2)/v[n-4]); v \\ G. C. Greubel, Feb 23 2019
(Magma) I:=[1, 1, -16, -644]; [n le 4 select I[n] else (36*Self(n-1) *Self(n-3) - 68*Self(n-2)^2)/Self(n-4): n in [1..20]]; // G. C. Greubel, Feb 23 2019
(Sage)
def a(n):
    if (n==0): return 1
    elif (n==1): return 1
    elif (n==2): return -16
    elif (n==3): return -644
    else: return (36*a(n-1)*a(n-3) - 68*a(n-2)^2)/a(n-4)
[a(n) for n in (1..20)] # G. C. Greubel, Feb 23 2019
(GAP) a:=[1, 1, -16, -644];; for n in [5..20] do a[n]:=(36*a[n-1]*a[n-3] - 68*a[n-2]^2)/a[n-4]; od; a; # G. C. Greubel, Feb 23 2019

Crossrefs

Cf. A157005, A157101, A162547.

Sequence in context: A139166 A128048 A197670 * A328274 A249950 A334734

Adjacent sequences: A162543 A162544 A162545 * A162547 A162548 A162549

Keyword

easy,sign

Author

Paul Barry, Jul 05 2009

Status

approved