A026058 a(n) = (d(n)-r(n))/2, where d = A026057 and r is the periodic sequence with fundamental period (0,0,1,0).
13, 25, 41, 63, 90, 123, 162, 209, 263, 325, 395, 475, 564, 663, 772, 893, 1025, 1169, 1325, 1495, 1678, 1875, 2086, 2313, 2555, 2813, 3087, 3379, 3688, 4015, 4360, 4725, 5109, 5513, 5937, 6383, 6850, 7339, 7850, 8385, 8943, 9525, 10131, 10763, 11420, 12103, 12812, 13549, 14313, 15105, 15925
Offset: 4
Links
- Index entries for linear recurrences with constant coefficients, signature (3,-3,1,1,-3,3,-1).
Crossrefs
Cf. A026057.
Formula
a(n) = - 0.125 - 0.125*( - 1)^n + 0.25*cos(n*Pi/2) + (n + 4)*(n^2 + 20*n + 39)/12. [Richard Choulet, Dec 13 2008]
G.f.: x^4*( 13-14*x+5*x^2+2*x^3-14*x^4+15*x^5-5*x^6 ) / ( (1+x)*(x^2+1)*(x-1)^4 ). - R. J. Mathar, Jun 22 2013