OFFSET
1,3
COMMENTS
a(n) is a lower bound for the number of fundamental invariants of binary forms of degree n+2 - see Kac. A lower estimate for a(n) is given by Dixmier et al.
a(n) is the number of nonempty multisets of positive integers < n such that their sum modulo n is zero and that no proper nonempty subset has this property. - George B. Salomon, Sep 29 2019
LINKS
Vakhtang Tsiskaridze, Table of n, a(n) for n = 1..64, computed by a Pascal code (1994, unpublished)
J. Dixmier, P. Erdős and J.-L. Nicolas, Sur le nombre d'invariants fondamentaux des formes binaires, C. R. Acad. Sci. Paris Ser. I Math. 305 (1987), no. 8, 319-322.
John C. Harris and David L. Wehlau, Non-negative Integer Linear Congruences, Indag. Math. 17 (2006) 37-44.
V. Kac, Root systems, representations of quivers and invariant theory, Invariant theory (Montecatini, 1982), 74-108, Lecture Notes in Math., 996, Springer, Berlin, 1983.
Klaus Pommerening, The Indecomposable Solutions of Linear Congruences, arXiv:1703.03708 [math.NT], 2017.
EXAMPLE
a(3)=3 since 3+2*0=3, 1+2*1=3 and 0+2*3=6 are the only indecomposable nonnegative integer solutions to x_1+2x_2=0 (mod 3): all other nonnegative integer solutions have form x_1=p*3+q*1+r*0, x_2=p*0+q*1+r*3 for nonnegative integers p, q, r.
CROSSREFS
KEYWORD
nonn
AUTHOR
Mamuka Jibladze, Jun 28 2004
STATUS
approved