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 A091144 a(n) = binomial(n^2, n)/(1+(n-1)*n). 3
 1, 1, 2, 12, 140, 2530, 62832, 1997688, 77652024, 3573805950, 190223180840, 11502251937176, 779092434772236, 58448142042957576, 4811642166029230560, 431306008583779517040, 41820546066482630185200 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Diagonal of array T(n,k) = binomial(kn,n)/(1+(k-1)n). Number of paths up and left from (0,0) to (n^2-n,n) where x/y <= n-1 for all intermediate points. - Henry Bottomley, Dec 25 2003 Empirical: In the ring of symmetric functions over the fraction field Q(q, t), letting s(1^n) denote the Schur function indexed by (1^n), a(n) is equal to the coefficient of s(n) in nabla^(n)s(1^n) with q=t=1, where nabla denotes the "nabla operator" on symmetric functions, and s(n) denotes the Schur function indexed by the integer partition (n) of n. - John M. Campbell, Apr 06 2018 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 D. Merlini, R. Sprugnoli and M. C. Verri, The tennis ball problem, J. Combin. Theory, A 99 (2002), 307-344. FORMULA From Henry Bottomley, Dec 25 2003: (Start) a(n) = A014062(n)/A002061(n); a(n) = A062993(n-2, n); a(n) = A070914(n, n-1); a(n) = A071201(n, n^2-n); a(n) = A071201(n, n^2-n+1); a(n) = A071202(n, n^2-n+1). (End) MAPLE A091144 := proc(n)     binomial(n^2, n)/(1+n*(n-1)) ; end proc: # R. J. Mathar, Feb 14 2015 MATHEMATICA Table[Binomial[n^2, n] / (n (n - 1) + 1), {n, 0, 20}] (* Vincenzo Librandi, Apr 07 2018 *) PROG (PARI) a(n) = binomial(n^2, n)/(n*(n-1)+1); \\ Altug Alkan, Apr 06 2018 (MAGMA) [Binomial(n^2, n)/(1+(n-1)*n): n in [0..20]]; // Vincenzo Librandi, Apr 07 2018 (GAP) List([0..20], n->Binomial(n^2, n)/(1+(n-1)*n)); # Muniru A Asiru, Apr 08 2018 CROSSREFS Cf. A002061, A014062, A062993, A070914, A071201, A071202. Sequence in context: A330655 A093543 A287885 * A275829 A240387 A087800 Adjacent sequences:  A091141 A091142 A091143 * A091145 A091146 A091147 KEYWORD nonn,easy AUTHOR Paul Barry, Dec 22 2003 STATUS approved

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Last modified August 1 06:45 EDT 2021. Contains 346384 sequences. (Running on oeis4.)