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 A112521 Sequence related to NOR bracketings. 1
 0, 1, 0, 6, 4, 60, 84, 700, 1440, 8910, 23100, 120120, 360360, 1684956, 5552064, 24302520, 85101456, 357502860, 1302562404, 5333981796, 19947127200, 80408748420, 305922388200, 1221485157360, 4701015343440, 18664243014300 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS Conjecture: Starting with n=1, a(n) is the main diagonal of the array defined as T(1,1) = 1, T(i,j) = 0 if i<1 or j<1, T(n,k) = T(n,k-2) + T(n,k-1) -2*T(n-1,k-1) + T(n-1,k) + T(n-2,k). [From Gerald McGarvey, Oct 07 2008] LINKS FORMULA a(n) = Sum_{j=0..n} (-1)^(j-1)*C(2n-j-1, n-j)*C(2(j-1), j-1). - corrected by Peter Bala, Aug 19 2014 a(n) = n*A055392(n), n>1. PROG (PARI) a(n) = sum(j=0, n, (-1)^(j-1)*binomial(2*n-j-1, n-j)*binomial(2*(j-1), j-1)); \\ Michel Marcus, Aug 19 2014 CROSSREFS Cf. A055392. Sequence in context: A333813 A327370 A260716 * A192350 A308900 A239861 Adjacent sequences:  A112518 A112519 A112520 * A112522 A112523 A112524 KEYWORD easy,nonn AUTHOR Paul Barry, Sep 09 2005 STATUS approved

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Last modified June 23 18:45 EDT 2021. Contains 345402 sequences. (Running on oeis4.)