A064439 Numbers n such that sigma(n) - n - 1 = pi(n).

4, 55, 65, 95, 125, 145, 155, 185, 205, 2779, 2863, 55297, 174691, 174779, 487903, 1301989, 1302457, 5254751, 6383483, 23140961, 48267437, 59651051, 70111213, 70111247, 92514491, 199445641, 212210443, 514269523, 514269599, 21881358361, 1602278990111

Offset

1,1

Comments

a(32) > 3*10^12. - Giovanni Resta, Mar 31 2017

Links

Table of n, a(n) for n=1..31.

Mathematica

Select[Range[10^5], DivisorSigma[1, #] - # - 1 == PrimePi[#] &] (* Giovanni Resta, Mar 31 2017 *)

Prog

(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)))
(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

Crossrefs

Cf. A000720, A048050.

Sequence in context: A048371 A077658 A217124 * A352510 A133218 A190441

Adjacent sequences: A064436 A064437 A064438 * A064440 A064441 A064442

Keyword

nonn

Author

Jason Earls, Oct 01 2001

Extensions

More terms from Klaus Brockhaus, Oct 05 2001. No further term < 800000.

a(16)-a(17) from Harry J. Smith, Sep 14 2009

a(18)-a(29) from Donovan Johnson, Feb 09 2013

a(30)-a(31) from Giovanni Resta, Mar 31 2017

Status

approved