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 A005569 Number of walks on square lattice. (Formerly M3654) 0
 4, 34, 308, 3024, 31680, 349206, 4008004, 47530912, 579058896, 7215393640, 91644262864, 1183274479040, 15497363512800, 205519758825150, 2755739674246500, 37314861293793600, 509727100259638800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS R. K. Guy, Letter to N. J. A. Sloane, May 1990 R. K. Guy, Catwalks, sandsteps and Pascal pyramids, J. Integer Sequences, Vol. 3 (2000), Article #00.1.6. FORMULA G.f.: 4_F_3 ( [ 2, 17/5, 5/2, 3/2 ]; [ 4, 5, 12/5 ];16 x ). a(n)(n-1)(n+2)(n+3)(5n+2) = a(n-1)4n(2n-1)(2n+1)(5n+7), n>1. - Michael Somos, Mar 04 2003 PROG (PARI) a(n)=4*if(n<2, n==1, a(n-1)*n*(2*n-1)*(2*n+1)*(5*n+7)/((n-1)*(n+2)*(n+3)*(5*n+2))) CROSSREFS Sequence in context: A201684 A155628 A036352 * A232910 A208215 A025572 Adjacent sequences:  A005566 A005567 A005568 * A005570 A005571 A005572 KEYWORD nonn,walk,easy AUTHOR STATUS approved

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Last modified December 15 00:30 EST 2019. Contains 329988 sequences. (Running on oeis4.)