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A007575 Number of stable towers of 2 X 2 LEGO blocks.
(Formerly M2675)
2
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; text; internal format)
OFFSET

0,2

REFERENCES

Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 65.

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.

LINKS

Ray Chandler, Table of n, a(n) for n = 0..2098 (terms < 10^1000)

P. J. S. Watson, On "LEGO" towers, J. Rec. Math., 12 (No. 1, 1979-1980), 24-27. (Annotated scanned copy)

Index entry for sequences related to LEGO blocks

FORMULA

a(n) ~ 3^(n+1) / sqrt(Pi*n). - Vaclav Kotesovec, Jul 11 2018

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); # Søren Eilers

CROSSREFS

Cf. A007576.

Sequence in context: A090378 A007180 A059506 * A026299 A183117 A183124

Adjacent sequences:  A007572 A007573 A007574 * A007576 A007577 A007578

KEYWORD

nonn

AUTHOR

Simon Plouffe and N. J. A. Sloane, Robert G. Wilson v

STATUS

approved

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Last modified January 23 01:30 EST 2020. Contains 331166 sequences. (Running on oeis4.)