%I #3 Mar 30 2012 17:37:54
%S 1,3,4,8,9,15,21,33,35,39,51,57,69,70,87,93,111,123,129,141,159,177,
%T 183,201,213,219,237,249,267,291,303,309,321,327,339,381,393,411,417,
%U 447,453,471,489,501,519,537,543,573,579,591,597,633,669,681,687,699,717
%N Values of n for which A000224(n)=Ceiling[(n+1)/3]; A000224(n) is the number of squares mod n.
%C Conjecture. If n>2 and a(n) is a multiple of 3, then a(n)/3 is a prime; further, all odd primes are given as a(n)/3 for some n. (This has been verified up to n=2000.)
%Y Cf. A000224, A123723.
%K nonn
%O 1,2
%A _John W. Layman_, Oct 09 2006