OFFSET
1,2
REFERENCES
M. V. Lawson, Inverse Semigroups: The Theory of Partial Symmetries. Singapore: World Scientific, 1999.
E. S. Lyapin, Semigroups. Providence, RI: Amer. Math. Soc., 1974.
LINKS
Alan Weinstein, Groupoids: Unifying Internal and External Symmetry, Not. Amer. Math. Soc. 43, 744-752, 1996.
Eric Weisstein et al., Inverse Semigroup.
FORMULA
a(n) = Sum_{i=1..n} A001428(i).
EXAMPLE
a(7) = 1195 = 1 + 2 + 5 + 16 + 52 + 208 + 911.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Jonathan Vos Post, May 11 2006
EXTENSIONS
More terms from the data at A001428 added by Amiram Eldar, May 03 2023
STATUS
approved