OFFSET
1,2
COMMENTS
Moree gives an effective version, see Theorem 1.
LINKS
Paul Erdős, Über die Primzahlen gewisser arithmetischer Reihen, Math. Z. 39 (1935), pp. 473-491. [alternate link]
Martin Klazar, Analytic and Combinatorial Number Theory II (lecture notes). See section 2.3, Erdős's partial proof of Dirichlet's theorem.
P. Moree, Bertrand's postulate for primes in arithmetical progressions, Computers & Mathematics with Applications 26:5 (1993), pp. 35-43.
FORMULA
Numbers k such that Sum_{p < k, p does not divide k} 1/p < 1.
EXAMPLE
15 is in the sequence since 1/2 + 1/7 + 1/11 + 1/13 = 1623/2002 < 1.
PROG
(PARI) is(n)=if(n>840, 0, my(s); forprime(p=2, n-1, if(n%p, s+=1/p)); s<1)
CROSSREFS
KEYWORD
nonn,fini,full
AUTHOR
Charles R Greathouse IV, Nov 23 2017
STATUS
approved