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 A065523 Numbers n such that sigma(n) is a prime power (A025475). 1
 3, 7, 21, 31, 81, 93, 127, 217, 381, 400, 651, 889, 2667, 3937, 8191, 11811, 24573, 27559, 57337, 82677, 131071, 172011, 253921, 393213, 524287, 761763, 917497, 1040257, 1572861, 1777447, 2752491, 3120771, 3670009, 4063201, 5332341 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Donovan Johnson, Table of n, a(n) for n = 1..80 MATHEMATICA s[n_] := DivisorSigma[1, n ]; Select[ Range[2, 10^6], !PrimeQ[ s[ # ]] && Mod[ s[ # ], s[ # ] - EulerPhi[ s[ # ]]] == 0 & ] CROSSREFS A proper subset of A065496. Sequence in context: A003585 A108102 A357898 * A046528 A018572 A018641 Adjacent sequences: A065520 A065521 A065522 * A065524 A065525 A065526 KEYWORD nonn AUTHOR Robert G. Wilson v, Nov 27 2001 EXTENSIONS a(31)-a(35) from Donovan Johnson, Sep 05 2008 STATUS approved

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Last modified December 3 20:26 EST 2022. Contains 358543 sequences. (Running on oeis4.)