OFFSET
1,1
COMMENTS
The negative Pell equation x^2 - q*y^2 = -1, hence q = (x^2 + 1)/y^2.
Primes p = q are A002496.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
EXAMPLE
For prime p = 349 = 18^2 + 5^2 is q = (18^2 + 1)/5^2 = 13 prime < p.
PROG
(PARI) list(lim)=my(v=List(), x2, q, y, p); for(x=1, sqrtint(lim\4), x2=4*x^2; [q, y]=core(x2+1, 1); p=x2+y^2; if(q<p && p<=lim && isprime(q) && isprime(p), listput(v, p))); Set(v) \\ Charles R Greathouse IV, Feb 14 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski and Altug Alkan, Feb 12 2017
STATUS
approved