OFFSET
1,1
COMMENTS
Consists of those primes congruent to 1, 5, 9 (mod 20) together with the squares of those primes congruent to -1, -3, -7, -9 (mod 20). Suppose n appears in this sequence. Then the number of prime elements of norm n is 2 if n is 5 or a square and 4 otherwise.
REFERENCES
David A. Cox, Primes of the form x^2+ny^2, Wiley, 1989.
A. Frohlich and M. J. Taylor, Algebraic number theory, Cambridge university press, 1991.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..10000
PROG
(PARI) list(lim)=my(v=List([5]), t); forprime(p=29, lim, t=p%20; if(t==1||t==9, listput(v, p))); forprime(p=11, sqrtint(lim\1), t=p%20; if(t==11||t==13||t==17||t==19, listput(v, p^2))); Set(v) \\ Charles R Greathouse IV, Feb 09 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Boddington, Feb 02 2004
EXTENSIONS
a(43) corrected by Charles R Greathouse IV, Feb 09 2017
STATUS
approved