OFFSET
1,2
REFERENCES
Hans Riesel, Prime Numbers and Computer Methods for Factorization, 2nd ed., Birkhauser, The distribution of primes between the two series 4n+1 and 4n+3, pages 73-77, with graphs.
LINKS
Marc Deléglise, Pierre Dusart, and Xavier-Francois Roblot, Counting primes in residue classes, Math. Comp. 73 (2004), no. 247, 1565-1575.
Carlos Rivera, Puzzle 256, Jack Brennen old records, The Prime Puzzles & Problems Connection.
FORMULA
EXAMPLE
a(1) = 1 because below 10^1 3 and 7 are 3 mod 4 and 5 is 1 mod 4 and the difference is 2-1=1.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Enoch Haga, Feb 23 2004
EXTENSIONS
a(17)-a(20) from Marc Deleglise, Jun 28 2007
STATUS
approved