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 A100517 Denominator of Sum_{k=0..n} 1/binomial(n,k)^2. 4
 1, 1, 4, 9, 72, 10, 3600, 1575, 2800, 1764, 14112, 13475, 34927200, 2316600, 192192, 4459455, 4994589600, 262061800, 735869534400, 17476901442, 422721728, 353723760, 31127690880, 10150725585, 59637542956992, 2205530434800, 155748568976000, 50956005028500 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES H. W. Gould, Combinatorial Identities, Morgantown, 1972, p. 50, formula (5.2). LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 FORMULA a(n) = denominator( 3*(n+1)^2/((n+2)*(2*n+3)*Catalan(n+1)) * Sum_{k=1..n+1} binomial(2*k, k)/k ). - G. C. Greubel, Jun 24 2022 EXAMPLE 1, 2, 9/4, 20/9, 155/72, 21/10, 7441/3600, 3224/1575, 5697/2800, 3575/1764, 28523/14112, 27183/13475, 70357417/34927200, 4661447/2316600, ... = A100516/A100517 MATHEMATICA Table[Sum[1/Binomial[n, k]^2, {k, 0, n}], {n, 0, 30}]//Denominator (* Harvey P. Dale, Apr 01 2019 *) PROG (Magma) [Denominator( (&+[1/Binomial[n, k]^2: k in [0..n]]]) ): n in [0..40]]; // G. C. Greubel, Jun 24 2022 (SageMath) [denominator(sum(1/binomial(n, k)^2 for k in (0..n))) for n in (0..40)] # G. C. Greubel, Jun 24 2022 (PARI) a(n) = denominator(sum(k=0, n, 1/binomial(n, k)^2)); \\ Michel Marcus, Jun 24 2022 CROSSREFS Cf. A000108, A046825, A046826, A100516, A100518, A100519. Sequence in context: A220189 A122956 A041777 * A327579 A041597 A041030 Adjacent sequences: A100514 A100515 A100516 * A100518 A100519 A100520 KEYWORD nonn,frac AUTHOR N. J. A. Sloane, Nov 25 2004 STATUS approved

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Last modified December 3 23:05 EST 2022. Contains 358543 sequences. (Running on oeis4.)