A188212 - OEIS

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A188212

Number of nondecreasing arrangements of 4 numbers in -(n+2)..(n+2) with sum zero.

18, 33, 55, 86, 126, 177, 241, 318, 410, 519, 645, 790, 956, 1143, 1353, 1588, 1848, 2135, 2451, 2796, 3172, 3581, 4023, 4500, 5014, 5565, 6155, 6786, 7458, 8173, 8933, 9738, 10590, 11491, 12441, 13442, 14496, 15603, 16765, 17984, 19260, 20595, 21991

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OFFSET

1,1

COMMENTS

Row 4 of A188211.

LINKS

R. H. Hardin, Table of n, a(n) for n = 1..200

FORMULA

Empirical: a(n) = 3*a(n-1) - 3*a(n-2) + 2*a(n-3) - 3*a(n-4) + 3*a(n-5) - a(n-6).

Empirical g.f.: x*(18 - 21*x + 10*x^2 - 16*x^3 + 21*x^4 - 8*x^5) / ((1 - x)^4*(1 + x + x^2)). - Colin Barker, Apr 27 2018

EXAMPLE

Some solutions for n=3: