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A003487
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a(n) = a(n-1)^2 - 2.
(Formerly M3926)
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3
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OFFSET
| 0,1
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REFERENCES
| N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Index entries for sequences of form a(n+1)=a(n)^2 + ...
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FORMULA
| a(n) = ceiling(c^(2^n)) where c=(5+sqrt(21))/20 is the largest root of x^2-5x+1=0. - Benoit Cloitre, Dec 03, 2002
a(n) = 2*T(2^n,5/2) where T(n,x) is the Chebyshev polynomial of the first kind. [From Leonid Bedratyuk (leonid.uk(AT)gmail.com), Mar 17 2011]
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MAPLE
| a:= n-> simplify (2*ChebyshevT(2^n, 1/2*5), 'ChebyshevT'):
seq (a(n), n=0..7);
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CROSSREFS
| Cf. A001566 (starting with 3), A003010 (starting with 4), A003423 (starting with 6).
Sequence in context: A018899 A080990 A172036 * A055490 A002811 A177134
Adjacent sequences: A003484 A003485 A003486 * A003488 A003489 A003490
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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