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Donovan Johnson, Table of n, a(n) for n = 1..500
sigma(15) = 24 = phi(3 * 15), so 15 is a term of the sequence.
Select[ Range, EulerPhi[3# ] == DivisorSigma[1, # ] &]
(PARI) is(n)=sigma(n)==eulerphi(3*n) \\ Charles R Greathouse IV, Dec 09 2013
Sequence in context: A027442 A208728 A219689 * A271733 A241282 A249056
Adjacent sequences: A074888 A074889 A074890 * A074892 A074893 A074894
Joseph L. Pe, Sep 13 2002
Edited and extended by Robert G. Wilson v, Sep 17 2002