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%I #20 Dec 15 2017 17:35:39
%S 4,55,65,95,125,145,155,185,205,2779,2863,55297,174691,174779,487903,
%T 1301989,1302457,5254751,6383483,23140961,48267437,59651051,70111213,
%U 70111247,92514491,199445641,212210443,514269523,514269599,21881358361,1602278990111
%N Numbers n such that sigma(n) - n - 1 = pi(n).
%C a(32) > 3*10^12. - _Giovanni Resta_, Mar 31 2017
%t Select[Range[10^5], DivisorSigma[1, #] - # - 1 == PrimePi[#] &] (* _Giovanni Resta_, Mar 31 2017 *)
%o (PARI) sig(n) = sigma(n)-n-1; pi(x, c=0) = forprime(p=2,x,c++); c for(n=1,10^8, if(sig(n)==pi(n),print(n)))
%o (PARI) { n=0; for (m=1, 10^9, if ((sigma(m) - m - 1)==primepi(m), write("b064439.txt", n++, " ", m); if (n==100, break)) ) } \\ _Harry J. Smith_, Sep 14 2009
%Y Cf. A000720, A048050.
%K nonn
%O 1,1
%A _Jason Earls_, Oct 01 2001
%E More terms from _Klaus Brockhaus_, Oct 05 2001. No further term < 800000.
%E a(16)-a(17) from _Harry J. Smith_, Sep 14 2009
%E a(18)-a(29) from _Donovan Johnson_, Feb 09 2013
%E a(30)-a(31) from _Giovanni Resta_, Mar 31 2017
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