OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,0,2,-2,0,-1,1).
FORMULA
G.f.: x*(x^6-4*x^3-x^2-x-1) / ((x-1)^3*(x^2+x+1)^2). [Colin Barker, Dec 13 2012]
EXAMPLE
a(4) = 9 because 9 is the largest number k such that the equation 5*x_1 + 6*x_2 + 7*x_3 + 9*x_4 = k has no solution for any nonnegative x_i (in other words, for every k > 9 there exist one or more solutions).
MATHEMATICA
Table[FrobeniusNumber[{n + 1, n + 2, n + 3, n + 4}], {n, 1, 100}]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Artur Jasinski, Apr 05 2008
STATUS
approved