A165918 a(n) = number of squarefree quadratic non-residues of n.

0, 0, 1, 2, 2, 2, 3, 5, 4, 3, 4, 7, 5, 5, 7, 10, 7, 8, 6, 11, 10, 8, 10, 15, 10, 8, 11, 15, 10, 12, 12, 18, 15, 11, 15, 21, 13, 13, 19, 25, 16, 19, 14, 25, 24, 17, 19, 29, 19, 18, 21, 28, 17, 22, 25, 33, 25, 18, 19, 35, 21, 22, 32, 34, 28, 29, 20, 36, 33, 31, 29, 44, 26, 23

Offset: 1

Author

Christopher Hunt Gribble, Sep 30 2009

Keywords

• nonn

Links

• C. H. Gribble, Table of n, a(n) for n=1,...,1000.

Crossrefs

Cf. A165916.

Programs

PARI

squares(n) = {local(s = Set()); for (j=1, n, s = setunion(s, Set(j^2 % n));); return (s);}
qnonr(n) = {local(s = Set()); sq = squares(n);for (j=0, n-1, if (length(setintersect(Set(j), sq))==0, s = setunion(s, Set(j)));); return (s);}
a(n) = {s = Set(); qnr = qnonr(n); for (j=1, #qnr, if (issquarefree(eval(qnr[j])), s = setunion(s, Set(qnr[j])));); return (#s);}  \\ Michel Marcus, Jul 23 2013

Extensions

a(1) added by Christopher Hunt Gribble, Oct 05 2009