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A032087
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Number of reversible strings with n beads of 4 colors. If more than 1 bead, not palindromic.
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1
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4, 6, 24, 120, 480, 2016, 8064, 32640, 130560, 523776, 2095104, 8386560, 33546240, 134209536, 536838144, 2147450880, 8589803520, 34359607296, 137438429184, 549755289600, 2199021158400, 8796090925056
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| C. G. Bower, Transforms (2)
Elizabeth Wilmer, Notes on Stephan's conjectures 72, 73 and 74
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FORMULA
| "BHK" (reversible, identity, unlabeled) transform of 4, 0, 0, 0...
a(2n+1) = 2^(4n+1) - 2^(2n+1), a(2n) = 2^(4n-1) - 2^(2n) + 2^(2n-1), a(1)=4.
a(n)=4*a(n-1)+4*a(n-2)-16*a(n-3), n>4. G.f.: 2*x*(-5*x+2-8*x^2+32*x^3)/((2*x+1)*(2*x-1)*(4*x-1)). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Mar 20 2009]
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CROSSREFS
| Cf. A088037.
Cf.: A026337 (bisection). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Mar 20 2009]
Sequence in context: A067001 A057343 A000287 * A165164 A136591 A009459
Adjacent sequences: A032084 A032085 A032086 * A032088 A032089 A032090
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KEYWORD
| nonn
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AUTHOR
| Christian G. Bower (bowerc(AT)usa.net)
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