OFFSET
1,2
REFERENCES
R. Fröberg, C. Gottlieb and R. Häggkvist, "On numerical semigroups", Semigroup Forum, 35 (1987), 63-83 (for definition of Frobenius number).
LINKS
Eric Weisstein's World of Mathematics, Lucas numbers.
FORMULA
a(n) = (L(n)-1)*(L(n+1)-1)-1 where L(n) = A000204(n).
a(n) = A002878(n)-A000204(n+2)+(-1)^n, for n>1. [Ralf Stephan, Nov 15 2010, index shifted by R. J. Mathar, Nov 16 2010]
G.f.: x^2*(5+2*x+3*x^2-x^4)/(1+x)/(1-3*x+x^2)/(1-x-x^2). [Colin Barker, Feb 17 2012]
EXAMPLE
a(3) = 17 because the 3rd and 4th Lucas numbers are 4 and 7, so
a(3) = (4-1)*(7-1)-1 = 17. Or, a(3)=17 because 17 is the largest positive
integer that is not a nonnegative linear combination of 4 and 7.
MAPLE
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, May 01 2005
STATUS
approved