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A007575
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Number of stable towers of 2 X 2 LEGO blocks.
(Formerly M2675)
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1
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1, 3, 7, 19, 53, 149, 419, 1191, 3403, 9755, 28077, 81097, 234861, 681697, 1982723, 5777375, 16861521, 49281525, 144222987, 422566835, 1239423303, 3638872529, 10693065215, 31448140529, 92558787745, 272612601065, 803448576111
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
P. J. S. Watson, On "LEGO" towers, J. Rec. Math., 12 (No. 1, 1979-1980), 24-27.
Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 65.
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MAPLE
| seq(sum(coeff(product(1+x^k+x^(2*k), k=1..n), x, l), l=n*(n+1)/2-n..n*(n+1)/2+n), n=0..20); - Soren Eilers.
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CROSSREFS
| Cf. A007576.
Sequence in context: A090378 A007180 A059506 * A026299 A183117 A183124
Adjacent sequences: A007572 A007573 A007574 * A007576 A007577 A007578
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KEYWORD
| nonn
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AUTHOR
| Simon Plouffe, N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com)
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