OFFSET
1,2
PROG
(PARI) isok(n) = {my(f=factor(n)); (#f~ == 0) || (bigomega(n) < f[1, 1]); }
a(n) = sum(k=1, n, isok(k)); \\ Michel Marcus, Feb 05 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 04 2004
STATUS
approved