A170834 a(n) = 5^(floor(n/2))+5^(floor(n/2)-1)-5^(floor((n-1)/3)).

5, 5, 25, 25, 145, 125, 725, 725, 3625, 3625, 18625, 18125, 93125, 93125, 465625, 465625, 2340625, 2328125, 11703125, 11703125, 58515625, 58515625, 292890625, 292578125, 1464453125, 1464453125, 7322265625, 7322265625, 36619140625, 36611328125, 183095703125

Offset

2,1

Links

Table of n, a(n) for n=2..32.

R. P. Stanley, Problem 11348, Amer. Math. Monthly, 117 (2010), 87-88.

Index entries for linear recurrences with constant coefficients, signature (0,5,5,0,-25).

Formula

a(n) = 5*a(n-2)+5*a(n-3)-25*a(n-5). G.f.: -5*x^2*(x^4+5*x^3-x-1) / ((5*x^2-1)*(5*x^3-1)). - Colin Barker, Jul 26 2013

Crossrefs

Cf. A170831, A170832, A170833.

Sequence in context: A162962 A074872 A056451 * A154630 A245520 A245130

Adjacent sequences: A170831 A170832 A170833 * A170835 A170836 A170837

Keyword

nonn,easy

Author

N. J. A. Sloane, Dec 30 2009

Status

approved