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A025254
a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-3)*a(3) for n >= 4.
1
3, 1, 1, 3, 10, 34, 118, 417, 1497, 5448, 20063, 74649, 280252, 1060439, 4040413, 15488981, 59701236, 231236830, 899559100, 3513314664, 13770811198, 54152480421, 213585706927, 844723104691, 3349274471386, 13310603555085, 53012829376985
OFFSET
1,1
FORMULA
G.f.: (1 + 3*x + x^2 - sqrt(x^4 + 2*x^3 + 7*x^2 - 6*x + 1))/(2*x). - Vaclav Kotesovec, Mar 02 2014
Recurrence: (n+1)*a(n) = 3*(2*n-1)*a(n-1) - 7*(n-2)*a(n-2) - (2*n-7)*a(n-3) - (n-5)*a(n-4). - Vaclav Kotesovec, Mar 02 2014
MATHEMATICA
CoefficientList[Series[(1+3*x+x^2-Sqrt[x^4+2*x^3+7*x^2-6*x+1])/(2*x), {x, 0, 20}], x] (* Vaclav Kotesovec, Mar 02 2014 *)
CROSSREFS
Cf. A178578.
Sequence in context: A014516 A247306 A016563 * A245537 A277198 A242735
KEYWORD
nonn
STATUS
approved