A026739 Number of subgroups L of Z^n with the property that for every a in Z^n there exists precisely one b in L with d(a,b) <= 1. Here d denotes Euclidean distance.

1, 1, 2, 8, 72, 384, 3840, 80640, 645120, 10321920, 309657600, 3715891200, 102187008000, 3310859059200, 51011754393600, 1428329123020800, 68559797904998400, 1942527607308288000

Offset

0,3

Links

Table of n, a(n) for n=0..17.

Formula

a(n) = 2^n*n!*sum(1/|Aut(G)|), where the sum is over all isomorphism classes of Abelian groups of order 2*n+1.

Crossrefs

Sequence in context: A180687 A356811 A296629 * A060635 A377401 A364408

Adjacent sequences: A026736 A026737 A026738 * A026740 A026741 A026742

Keyword

easy,nonn

Author

Paul Boddington, Jan 26 2004

Status

approved