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Search: id:A005569
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| A005569 |
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Number of walks on square lattice.
(Formerly M3654)
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+0
1
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| 4, 34, 308, 3024, 31680, 349206, 4008004, 47530912, 579058896, 7215393640, 91644262864, 1183274479040, 15497363512800, 205519758825150, 2755739674246500, 37314861293793600, 509727100259638800
(list; graph; listen)
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OFFSET
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1,1
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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R. K. Guy, Catwalks, Sandsteps and Pascal Pyramids, J. Integer Seqs., Vol. 3 (2000), #00.1.6
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FORMULA
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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
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PROGRAM
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(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)))
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CROSSREFS
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Sequence in context: A116430 A155628 A036352 this_sequence A025572 A093137 A107350
Adjacent sequences: A005566 A005567 A005568 this_sequence A005570 A005571 A005572
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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