OFFSET
1,13
LINKS
Jianing Song, Table of n, a(n) for n = 1..10000
EXAMPLE
There are 11 primes <= 100 that are congruent to 1 modulo 3, namely 7, 13, 19, 31, 37, 43, 61, 67, 73, 79, 97, so a(100) = 11.
PROG
(PARI) a(n) = sum(i=1, n, isprime(i) && (i%3==1))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Jianing Song, Apr 28 2021
STATUS
approved