OFFSET
1,3
COMMENTS
A numerical semigroup is a set of natural numbers closed under addition. Its Frobenius number is the largest number not in it. In the case of a semigroup generated by two relatively prime numbers a and b, its Frobenius number is ab-a-b, which is always odd.
LINKS
David Wasserman, Table of n, a(n) for n = 1..300
J. C. Rosales, P. A. Garcia-Sanchez and J. I. Garcia-Garcia, Every positive integer is the Frobenius number of a numerical semigroup with three generators, Math. Scand. 94 (2004), no. 1, 5-12.
EXAMPLE
a(9) = 3: the 3 semigroups generated by {2, 19}, {3, 10} and {4, 7} have Frobenius number 17.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Corina Flynn (Corinamachina(AT)hotmail.com), May 07 2004
EXTENSIONS
Edited and extended by David Wasserman, Sep 27 2006
STATUS
approved