A217779 Expansion of (1-4x+4*x^2)/((1-5x+5*x^2)*(1-3x+x^2)).

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

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.

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.