OFFSET
1,9
COMMENTS
Erdős proved that between any n > 7 and its double there are always at least two primes, one of form 4*k+1 and one of form 4*k+3.
REFERENCES
B. Schechter, "My Brain is Open: The Mathematical Journeys of Paul Erdős," Simon & Schuster, New York, 1998, p. 62.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
a[n_] := Module[{c = 0}, Do[If[Mod[k, 4] == 1 && PrimeQ[k], c++], {k, n, 2 n}]; c]; Array[a, 100] (* Amiram Eldar, Dec 16 2019 *)
PROG
(Magma) [#[p:p in PrimesInInterval(n, 2*n)| p mod 4 eq 1]:n in [1..110]]; // Marius A. Burtea, Dec 16 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, Jul 30 2003
STATUS
approved