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 A171638 Denominator of 1/(n-2)^2 - 1/(n+2)^2. 1
 0, 25, 9, 441, 64, 2025, 225, 5929, 576, 13689, 1225, 27225, 2304, 48841, 3969, 81225, 6400, 127449, 9801, 190969, 14400, 275625, 20449, 385641, 28224, 525625, 38025, 700569, 50176, 915849, 65025, 1177225, 82944, 1490841 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 COMMENTS Fifth column of an array of denominators related to the energies of the hydrogen spectrum, mentioned in A171522. At n=2, the defining formula has a pole and is replaced by 0 to conform with A171621 and A099761. 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). MAPLE A061037 := proc(n) 1/4-1/n^2 ; numer(%) ; end proc: A171621 := proc(n) if n mod 4 = 2 then 4*A061037(n) ; else A061037(n) ; end if; end proc: A171638 := proc(n) A171621(n)^2 ; end proc: seq(A171638(n), n=2..90) ; # R. J. Mathar, Apr 02 2011 MATHEMATICA Table[If[n == 2, 0, Denominator[1/(n-2)^2 - 1/(n+2)^2]], {n, 2, 50}] (* G. C. Greubel, Sep 20 2018 *) 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 Sequence in context: A224490 A226224 A181763 * A217432 A040604 A097440 Adjacent sequences:  A171635 A171636 A171637 * A171639 A171640 A171641 KEYWORD nonn,frac,easy AUTHOR Paul Curtz, Dec 13 2009 STATUS approved

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Last modified January 27 05:19 EST 2021. Contains 340451 sequences. (Running on oeis4.)