OFFSET
1,2
LINKS
P. Erdős and H. Heilbronn, On the addition of residue classes mod p, Acta Arithmetica 9 (1964), 149-159.
John E. Olson, An addition theorem modulo p, Journal of Combinatorial Theory 5 (1968), pp. 45-52.
FORMULA
For p = prime(n) > 3, sqrt(4p + 5) - 2 < a(n) <= sqrt(4p). The former bound is due to Erdős & Heilbronn and the latter to Olson.
PROG
(PARI) sumHitsAll(v, m)=my(u=[0], n); for(i=1, #v, n=v[i]; u=Set(concat(u, apply(j->(j+n)%m, u))); if(#u==m, return(1))); 0
a(n, p=prime(n))=for(s=sqrtint(4*p+2)-1, sqrtint(4*p)-1, forvec(v=vector(s, i, [1, p-1]), if(!sumHitsAll(v, p), next(2)), 2); return(s)); sqrtint(4*p)
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Charles R Greathouse IV, Jan 24 2018
EXTENSIONS
a(13) from Charles R Greathouse IV, Jan 27 2018
a(14)-a(22) from Bert Dobbelaere, Apr 20 2019
STATUS
approved