A026955 a(n) = Sum_{k=0..n} (k+1) * T(n,k), with T given by A026386.
1, 3, 8, 25, 60, 175, 400, 1125, 2500, 6875, 15000, 40625, 87500, 234375, 500000, 1328125, 2812500, 7421875, 15625000, 41015625, 85937500, 224609375, 468750000, 1220703125, 2539062500, 6591796875, 13671875000, 35400390625
Offset: 0
Links
- Andrew Howroyd, Table of n, a(n) for n = 0..1000
- Index entries for linear recurrences with constant coefficients, signature (0,10,0,-25).
Crossrefs
Cf. A026386.
Programs
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PARI
a(n) = if(n==0, 1, (n + 2) * (7 - 3*(-1)^n) * 5^floor(n/2) / 10) \\ Andrew Howroyd, Dec 27 2024
Formula
a(n) = (n + 2) * (7 - 3*(-1)^n) * 5^floor(n/2) / 10 for n > 0.
From Colin Barker, Oct 13 2012: (Start)
a(n) = 10*a(n-2) - 25*a(n-4) for n>4.
G.f.: (5*x^4-5*x^3-2*x^2+3*x+1)/(5*x^2-1)^2. (End)