OFFSET
1,2
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 1..57
L. Penso-Dolfin and C. D. Greenman, The Combinatorics of Tandem Duplication, arXiv:1402.0104v1 [math.CO], Feb 1, 2014.
FORMULA
a(n) = Product_{k=1..n} (4^k - (2*k+1)).
EXAMPLE
a(4) = (4^1 - (2*1+1)) * (4^2 - (2*2+1)) * (4^3 - (2*3+1)) * (4^4 - (2*4+1)).
MATHEMATICA
a[n_] := Product[4^k - 2 k - 1, {k, 1, n}]; Array[a, 12] (* Robert G. Wilson v, Feb 17 2014 *)
PROG
(PARI) a(n) = prod(k=1, n, 4^k - (2*k+1)); \\ Michel Marcus, Feb 04 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post, Feb 04 2014
EXTENSIONS
More terms from Michel Marcus, Feb 04 2014
STATUS
approved