A067788 Numbers n such that sigma(n) - phi(n) = pi(n).

1, 3, 49, 437, 11509, 3029573, 15714799, 15715171, 312616663, 45764089927, 2002330897321

Offset

1,2

Comments

pi(n) denotes the number of positive primes not exceeding n.

a(10) > 2*10^9. - Donovan Johnson, Dec 18 2009

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

Links

Table of n, a(n) for n=1..11.

Example

sigma(49) - phi(49) = 15 = pi(49), so 49 is a term of the sequence.

Mathematica

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

Prog

(PARI) isok(n) = sigma(n) - eulerphi(n) == primepi(n); \\ Michel Marcus, Oct 13 2014

Crossrefs

Sequence in context: A225317 A288527 A269630 * A167601 A061185 A182279

Adjacent sequences: A067785 A067786 A067787 * A067789 A067790 A067791

Keyword

nonn,more

Author

Joseph L. Pe, Feb 06 2002

Extensions

a(6)-a(9) from Donovan Johnson, Dec 18 2009

a(10)-a(11) from Giovanni Resta, Mar 31 2017

Status

approved