# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a222642 Showing 1-1 of 1 %I A222642 #13 Mar 25 2014 10:17:04 %S A222642 1,2,2,2,3,3,3,4,4,4,4,5,5,5,6,6,6,6,7,7,7,7,8,8,8,8,9,9,9,9,10,10,10, %T A222642 10,11,11,11,11,11,12,12,12,12,13,13,13,13,13,14,14,14,14,15,15,15,15, %U A222642 15,16,16,16,16,16,17,17,17,17,18,18,18,18,18,19,19 %N A222642 Integer nearest to (Li(n) - Li(sqrt(n))), where Li(x) = integral(0..x, dt/log(t)). %C A222642 Challenge: find the smallest n for which pi(n) < a(n), where pi(n) is the prime counting function. %H A222642 Arkadiusz Wesolowski, Table of n, a(n) for n = 2..10000 %H A222642 Wikipedia, Prime number theorem %t A222642 Table[Round[LogIntegral[n] - LogIntegral@Sqrt[n]], {n, 2, 74}] %o A222642 (PARI) a(n)=round(real(eint1(-log(n)/2)-eint1(-log(n)))) \\ _Charles R Greathouse IV_, Feb 27 2013 %Y A222642 Cf. A047743. %K A222642 nonn %O A222642 2,2 %A A222642 _Arkadiusz Wesolowski_, Feb 27 2013 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE