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A067787
Numbers n such that the number of primes not exceeding sigma(n) equals phi(n), i.e., pi(sigma(n)) = phi(n).
0
3, 9, 34, 190, 224, 606, 680, 4128, 6996, 8928
OFFSET
1,1
COMMENTS
No more terms up to 10^6. - Robert Israel, May 17 2017
No more terms up to 10^9. - Sean A. Irvine, Jan 05 2024
EXAMPLE
pi(sigma(9)) = pi(13) = 6 = phi(9).
MAPLE
select(n -> numtheory:-pi(numtheory:-sigma(n)) = numtheory:-phi(n), [$1..10^4]); # Robert Israel, May 17 2017
MATHEMATICA
pi[n_] := Module[{i = 0}, While[Prime[i + 1] <= n, i++ ]; i]; Do[If[pi[DivisorSigma[1, n]] == EulerPhi[n], Print[n]], {n, 1, 10^4}]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Joseph L. Pe, Feb 06 2002
STATUS
approved