A217782 Expansion of (1-x)*(1-2x)*(1-3x)/((1-5x+5*x^2)*(1-3x+x^2)).

1, 2, 6, 20, 69, 242, 857, 3054, 10930, 39236, 141153, 508598, 1834641, 6623450, 23926334, 86468052, 312587197, 1130277914, 4087621545, 14784539846, 53478888618, 193456813508, 699850536281, 2531866279710, 9159810802849, 33139021206962, 119894215708662

Offset: 0

Author

Philippe Deléham, Mar 24 2013

Keywords

• nonn
• easy

Comments

A diagonal of the square array A217770.

Links

• Index entries for linear recurrences with constant coefficients, signature (8, -21, 20, -5).

Crossrefs

Cf. A217770, A217777, A217778, A217779.

Formula

a(n) = A217770(n,n).

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) = 2, a(2) = 6, a(3) = 20.