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

1,4

Links

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

Prog

(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

Crossrefs

Cf. A165916.

Sequence in context: A082408 A270566 A182534 * A114639 A071867 A126337

Adjacent sequences: A165915 A165916 A165917 * A165919 A165920 A165921

Keyword

nonn

Author

Christopher Hunt Gribble, Sep 30 2009

Extensions

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

Status

approved