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A217779
Expansion of (1-4x+4*x^2)/((1-5x+5*x^2)*(1-3x+x^2)).
3
1, 4, 15, 56, 208, 768, 2821, 10320, 37639, 136972, 497652, 1805984, 6548425, 23729916, 85953823, 311240928, 1126753336, 4078394080, 14760382029, 53415642632, 193291233367, 699417041844, 2530731376540, 9156839587776, 33131242464913, 119873850697588
OFFSET
0,2
COMMENTS
A diagonal of the square array A217770.
FORMULA
a(n) = A217770(n,n+2).
a(n) = 8*a(n-1) - 21*a(n-2) + 20*a(n-3) - 5*a(n-4) for n>=4, a(0) = 1, a(1) = 4, a(2) = 15, a(3) = 56.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Philippe Deléham, Mar 24 2013
STATUS
approved