%I A007575 M2675
%S A007575 1,3,7,19,53,149,419,1191,3403,9755,28077,81097,234861,681697,1982723,
%T A007575 5777375,16861521,49281525,144222987,422566835,1239423303,3638872529,
%U A007575 10693065215,31448140529,92558787745,272612601065,803448576111
%N A007575 Number of stable towers of 2 X 2 LEGO blocks.
%D A007575 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A007575 P. J. S. Watson, On "LEGO" towers, J. Rec. Math., 12 (No. 1, 1979-1980), 
               24-27.
%D A007575 Clifford A. Pickover, A Passion for Mathematics, Wiley, 2005; see p. 
               65.
%p A007575 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.
%Y A007575 Cf. A007576.
%Y A007575 Sequence in context: A090378 A007180 A059506 this_sequence A026299 A078481 
               A104522
%Y A007575 Adjacent sequences: A007572 A007573 A007574 this_sequence A007576 A007577 
               A007578
%K A007575 nonn
%O A007575 1,2
%A A007575 Simon Plouffe, N. J. A. Sloane (njas(AT)research.att.com), Robert G. 
               Wilson v (rgwv(AT)rgwv.com)