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Search: id:A067787
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| A067787 |
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Numbers n such that the number of primes not exceeding sigma(n) equals phi(n), i.e. pi(sigma(n)) = phi(n). |
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1
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OFFSET
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1,1
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EXAMPLE
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pi(sigma(9)) = pi(13) = 6 = phi(9).
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MATHEMATICA
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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}]
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CROSSREFS
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Adjacent sequences: A067784 A067785 A067786 this_sequence A067788 A067789 A067790
Sequence in context: A085686 A084756 A009578 this_sequence A130491 A102865 A046697
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Feb 06 2002
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