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Search: id:A051786
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| A051786 |
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Propp's cubic recurrence: a(0) = a(1) = a(2) = a(3) = 1; a(n)=(1+a(n-1)*a(n-2)*a(n-3))/a(n-4). |
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+0
4
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| 1, 1, 1, 1, 2, 3, 7, 43, 452, 45351, 125920291, 60027819184831, 758397193749171922281611, 126403219004744354228963383975713263866432, 45699526286117471520994956894648733172150425791690122432447239675853643
(list; graph; listen)
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OFFSET
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0,5
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REFERENCES
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Jim Propp (propp(AT)math.wisc.edu), personal communication.
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FORMULA
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a(-n)=a(3+n). a(0)=a(1)=a(2)=a(3)=1. a(n+2)*a(n-2)=1+a(n+1)*a(n)*a(n-1).
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PROGRAM
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(PARI) {a(n)= if(n<0, n=3-n); if(n<4, 1, (a(n-1)*a(n-2)*a(n-3)+1)/a(n-4)) } /* Michael Somos Oct 16 2006 */
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CROSSREFS
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Cf. A005246.
Sequence in context: A000946 A091771 A072714 this_sequence A133400 A113845 A072713
Adjacent sequences: A051783 A051784 A051785 this_sequence A051787 A051788 A051789
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KEYWORD
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nonn,nice,easy
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AUTHOR
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Michael Somos
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EXTENSIONS
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Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, Jun 17 2007
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