A085521 a(n) = Product_{k=0..n} (2^(2k+1)+1).

1, 3, 27, 891, 114939, 58963707, 120816635643, 989850695823099, 32436417451427131131, 4251538544610908358733563, 2229034892015508532492061011707, 4674627210894999765441323226884370171, 39213619892958693087378972992951269575782139, 1315790781385749638968020894900792847245520205672187

Offset

-1,2

Comments

Partial products of A087289. - Michel Marcus, Feb 15 2014

Links

Vincenzo Librandi, Table of n, a(n) for n = -1..50

J. A. Thas, Old and new results on spreads and ovoids of finite classical polar spaces, Annals of Discrete Mathematics, Vol. 52, 1992, pp. 529-544, Combinatorics '90 — Recent Trends and Applications.

Formula

a(n) ~ c * 2^(n*(n+2)), where c = 2*QPochhammer(-1/2, 1/4) = 3.5167992012887276... . - Vaclav Kotesovec, Oct 19 2016

Mathematica

Table[Product[2^(2k+1)+1, {k, 0, n}], {n, -1, 15}] (* Harvey P. Dale, Jun 21 2011 *)
Table[QPochhammer[-2, 4, n + 1], {n, -1, 15}] (* Vladimir Reshetnikov, Oct 18 2016 *)

Prog

(PARI) a(n) = prod(k=0, n, 2^(2*k+1)+1); \\ Michel Marcus, Oct 17 2016

Crossrefs

Sequence in context: A194500 A012505 A331439 * A009066 A279832 A012012

Adjacent sequences: A085518 A085519 A085520 * A085522 A085523 A085524

Keyword

nonn

Author

N. J. A. Sloane, Jul 03 2003

Status

approved