OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
The first three primes == 3 (mod 4) are 3, 7, 11, but 3+7+11=21 is not prime.
The second, third and fourth primes == 3 (mod 4) are 7, 11, 19, and 7+11+19=37 is prime, so a(1)=37.
MAPLE
N:= 2000: # to use primes <= N that == 1 (mod 4)
P:= select(isprime, [seq(i, i=1..N, 4)]):
select(isprime, P[1..-3]+P[2..-2]+P[3..-1]);
MATHEMATICA
M = 2000;
P = Select[Range[3, M, 4], PrimeQ];
Select[P[[1;; -3]] + P[[2;; -2]] + P[[3;; -1]], PrimeQ] (* Jean-François Alcover, Apr 27 2019, from Maple *)
CROSSREFS
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, May 11 2018
STATUS
approved