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 A067144 Numbers k such that sigma(phi(k)) == 0 (mod k). 0
 1, 3, 15, 28, 255, 744, 1209, 2418, 20440, 65535, 548856, 2835756, 4059264, 4451832, 10890040, 13192608, 23001132, 23746333, 27474741, 54949482, 55385589, 110771178, 220174080, 222850677, 445701354, 4294967295, 16331433888, 18377794080, 94951936080 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sequence A018784 consists of solutions to sigma(phi(k))=k. If k is in A018784, or if k is odd and 2*k is in A018784 (e.g., k=1209), then k is in this sequence. Are there any other terms? Answer from Vim Wenders, Nov 11 2006: Yes. 23746333 is present. sigma(phi(23746333))/23746333 = 3 and neither 23746333 nor 47492666 is in A018784. LINKS Table of n, a(n) for n=1..29. PROG (PARI) isok(n) = sigma(eulerphi(n)) % n == 0; \\ Michel Marcus, Nov 20 2013 CROSSREFS Cf. A018784. Sequence in context: A222291 A015646 A242571 * A018784 A147344 A201434 Adjacent sequences: A067141 A067142 A067143 * A067145 A067146 A067147 KEYWORD nonn AUTHOR Benoit Cloitre, Feb 18 2002 EXTENSIONS Edited by Dean Hickerson, Feb 20 2002 More terms from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 28 2004 a(26)-a(28) from Donovan Johnson, Jul 06 2012 a(29) from Donovan Johnson, Nov 27 2013 STATUS approved

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Last modified December 1 05:26 EST 2023. Contains 367468 sequences. (Running on oeis4.)