OFFSET
1,2
COMMENTS
There are no terms <= 10^9 greater than a(3036) = 69808035, leading to the conjecture that the sequence is finite. If true, every sufficiently large number is expressible as x^2 + P*y^2 with x > 0, y > 1.
LINKS
Chris Boyd, Table of n, a(n) for n = 1..3036
EXAMPLE
Since 17 can be expressed as 3^2 + 2 * 2^2, it is not in the sequence.
No such expression exists for 18, hence it is in the sequence.
Since 19 can be expressed as 1^2 + 2 * 3^2, it is not in the sequence.
PROG
(PARI) test(n)={local(z, x, p, y); for(x=1, sqrtint(n), z=n-x^2; p=core(z); y=core(z, 1)[2]; if(isprime(p)&&y>1, return(1))); }
for(n=1, 300, if(test(n)==0, print1(n", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Chris Boyd, Sep 29 2013
STATUS
approved