OFFSET
1,1
COMMENTS
Number of safe primes with at most n digits; or a(10^n).
LINKS
Wikipedia, Safe prime
EXAMPLE
a(10^2) = a(100) = #{5, 7, 11, 23, 47, 59, 83} = 7
CROSSREFS
KEYWORD
nonn
AUTHOR
Krzysztof Ostrowski, Apr 09 2011
STATUS
approved