OFFSET
2,2
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 2..5000
Index entries for linear recurrences with constant coefficients, signature (0,5,0,-10,0,10,0,-5,0,1).
FORMULA
a(n) = (A171621(n))^2.
a(2*n+2) = A099761(n).
G.f.: -((x(25+9*x+316*x^2+19*x^3+70*x^4-5*x^5-36*x^6+x^7+9*x^8))/((-1+x)^5 (1+x)^5)). - Harvey P. Dale, Sep 07 2021
Sum_{n>=3} 1/a(n) = 19*Pi^2/192 - 115/144. - Amiram Eldar, Aug 14 2022
MAPLE
MATHEMATICA
Table[If[n == 2, 0, Denominator[1/(n-2)^2 - 1/(n+2)^2]], {n, 2, 50}] (* G. C. Greubel, Sep 20 2018 *)
LinearRecurrence[{0, 5, 0, -10, 0, 10, 0, -5, 0, 1}, {0, 25, 9, 441, 64, 2025, 225, 5929, 576, 13689}, 50] (* Harvey P. Dale, Sep 07 2021 *)
PROG
(Magma) [0] cat [Denominator((1/(n-2)^2 -1/(n+2)^2)): n in [3..350]]; // Bruno Berselli, Apr 05 2011
(PARI) for(n=2, 100, print1(if(n==2, 0, denominator(1/(n-2)^2 - 1/(n+2)^2)), ", ")) \\ G. C. Greubel, Sep 20 2018
CROSSREFS
KEYWORD
nonn,frac,easy
AUTHOR
Paul Curtz, Dec 13 2009
STATUS
approved