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Search: id:A005828
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| A005828 |
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a(n) = 2 a(n-1)^2 - 1.
(Formerly M3642)
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+0
2
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| 4, 31, 1921, 7380481, 108942999582721, 23737154316161495960243527681, 1126904990058528673830897031906808442930637286502826475521
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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An infinite coprime sequence defined by recursion. - Michael Somos Mar 14 2004
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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).
J. O. Shallit, personal communication.
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LINKS
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Anonymous, Fermat's rule for 3-fold perfect numbers
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PROGRAM
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(PARI) a(n)=if(n<1, 4*(n==0), 2*a(n-1)^2-1)
(PARI) a(n)=if(n<0, 0, subst(poltchebi(2^n), x, 4))
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CROSSREFS
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A001091(2^n)=a(n).
Sequence in context: A141827 A143077 A005841 this_sequence A084764 A061789 A103909
Adjacent sequences: A005825 A005826 A005827 this_sequence A005829 A005830 A005831
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KEYWORD
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nonn,easy
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AUTHOR
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Jeffrey Shallit
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