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)
Andrei Asinowski, Axel Bacher, Cyril Banderier, Bernhard Gittenberger, Analytic combinatorics of lattice paths with forbidden patterns, the vectorial kernel method, and generating functions for pushdown automata, Laboratoire d'Informatique de Paris Nord (LIPN 2019).
P. J. S. Watson, On "LEGO" towers, J. Rec. Math., 12 (No. 1, 1979-1980), 24-27. (Annotated scanned copy)
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
MATHEMATICA
Array[Sum[SeriesCoefficient[Product[1 + x^k + x^(2 k), {k, #}], {x, 0, j}], {j, # (# + 1)/2 - #, # (# + 1)/2 + #}] &, 27, 0] (* Michael De Vlieger, Feb 24 2020, after Maple *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved