N-rationality of a certain class of formal series
A series of the form (1 - ax + bx(k))(-1), where a is an element of N, b is an element of Z and k >= 2 is an element of N is N-rational if and only if (k - 1)(k-1) a(k) - k(k)b >= 0. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.
combinatorial problems formal languages