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A221859 Expansion of (1-3*x+x^2)*(1-2*x)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5). 1
1, 4, 15, 56, 209, 779, 2898, 10760, 39882, 147612, 545721, 2015721, 7440251, 27448008, 101217076, 373128151, 1375167467, 5067236766, 18669118971, 68774597447, 253334948791, 933111590565, 3436767111783, 12657552835178, 46616152422035, 171677402416052 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

A diagonal of the square array A223968.

LINKS

Table of n, a(n) for n=0..25.

FORMULA

a(n) = A223968(n,n+2).

G.f.: (1-3*x+x^2)*(1-2*x)/(1-9*x+28*x^2-35*x^3+15*x^4-x^5).

a(n) = 9*a(n-1) - 28*a(n-2) + 35*a(n-3) - 15*a(n-4) + a(n-5) with a(0) = 1, a(1) = 4, a(2) = 15, a(3) = 56, a(4) = 209.

CROSSREFS

Cf. A223968

Sequence in context: A217779 A191606 A242495 * A001353 A106707 A125905

Adjacent sequences:  A221856 A221857 A221858 * A221860 A221861 A221862

KEYWORD

nonn,easy

AUTHOR

Philippe Deléham, Apr 10 2013

STATUS

approved

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Last modified July 20 16:15 EDT 2019. Contains 325185 sequences. (Running on oeis4.)