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A178076 Sequence with a (4,-8) Somos-4 Hankel transform. 2
1, 0, 2, -2, 8, -20, 64, -200, 656, -2184, 7408, -25456, 88480, -310464, 1098304, -3912896, 14026752, -50557184, 183110400, -666079872, 2432399104, -8914099840, 32772922112, -120844493056, 446793362944, -1656004554752 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Hankel transform is A178077.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

FORMULA

a(n) = Sum_{k=0..floor(n/2)} ( (C(n-k,k)/(n-2k+1))*Sum_{i=0..k} C(k,i)*C(n-k-i-1,n-2k-i)*(-2)^(n-2k-i)*2^i*2^(k-i) ).

MATHEMATICA

Table[If[n == 0, 1, Sum[(Binomial[n-k, k]/(n-2*k+1))* Sum[Binomial[k, j]*Binomial[n-k-j-1, n-2*k-j]*(-2)^(n-2*k-j)*2^k, {j, 0, k}], {k, 0, Floor[n/2]}] + (1 + (-1)^n)/2], {n, 0, 100}] (* G. C. Greubel, Sep 18 2018 *)

PROG

(PARI) a(n) = sum(k=0, floor(n/2), sum(j=0, k, (binomial(n-k, k)/(n-2*k+1)) *binomial(k, j)*binomial(n-k-j-1, n-2*k-j)*(-2)^(n-2*k-j)*2^k));

for(n=0, 30, print1(a(n), ", ")) \\ G. C. Greubel, Sep 18 2018

CROSSREFS

Sequence in context: A080040 A060823 A330645 * A292476 A259807 A137774

Adjacent sequences:  A178073 A178074 A178075 * A178077 A178078 A178079

KEYWORD

easy,sign

AUTHOR

Paul Barry, May 19 2010

STATUS

approved

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Last modified July 26 02:06 EDT 2021. Contains 346294 sequences. (Running on oeis4.)