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
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
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