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 A137644 a(n) = Sum_{k=0..n} C(n+k,k)*C(n+k,n-k). 9
 1, 3, 16, 95, 591, 3780, 24620, 162423, 1081780, 7258053, 48982176, 332140328, 2261099491, 15444137880, 105789736896, 726426836103, 4998885106599, 34464824536500, 238017084356680, 1646234203000485, 11401464090042224, 79060352485691272, 548829398923188036 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Number of lattice paths from (0,0) to (n,n) using steps (1,0), (1,1), (0,1), (0,2). - Eric Werley, Jun 29 2011 Diagonal of rational function 1/(1 - (x + y + x*y + x^2)). - Gheorghe Coserea, Aug 31 2018 LINKS Indranil Ghosh, Table of n, a(n) for n = 0..500 FORMULA a(n) = 3F2( {-n, n+1, n+1}; {1/2, 1})( -(1/4) ). - Olivier Gérard, Apr 23 2009 G.f.: F'(x)/(1+F(x)), where F(x)=x*(1+F(x))/(1-F(x)-F(x)^2). - Vladimir Kruchinin, Mar 24 2012 a(n) = A063967(n,n). - Alois P. Heinz, Oct 11 2017 EXAMPLE The triangle of number of lattice paths from (0,0) to (n,k) using steps (1,0), (1,1), (0,1), (0,2) begins:   1;   1,  3;   1,  5,  16;   1,  7,  29,  95;   1,  9,  46, 179,  591;   1, 11,  67, 303, 1140,  3780;   1, 13,  92, 475, 2010,  7405, 24620;   1, 15, 121, 703, 3309, 13427, 48761, 162423;   1, 17, 154, 995, 5161, 22892, 90241, 324317, 1081780; This sequence is the diagonal. - Joerg Arndt, Jul 01 2011 MATHEMATICA Table[ HypergeometricPFQ[{-n, 1 + n, 1 + n}, {1/2, 1}, -(1/4)], {n, 0, 20}] (* Olivier Gérard, Apr 23 2009 *) Table[Sum[Binomial[n+k, k]Binomial[n+k, n-k], {k, 0, n}], {n, 0, 20}] (* Harvey P. Dale, Aug 03 2011 *) PROG (PARI) a(n)=sum(k=0, n, binomial(n+k, k)*binomial(n+k, n-k)) (PARI) /* same as in A092566 but use */ steps=[[1, 0], [1, 1], [0, 1], [0, 2]]; /* Joerg Arndt, Jun 30 2011 */ CROSSREFS Cf. A063967. Sequence in context: A213229 A323968 A074555 * A114174 A181067 A006347 Adjacent sequences:  A137641 A137642 A137643 * A137645 A137646 A137647 KEYWORD nonn AUTHOR Paul D. Hanna, Jan 31 2008 STATUS approved

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Last modified February 19 00:57 EST 2020. Contains 332028 sequences. (Running on oeis4.)