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%I #24 Feb 10 2021 21:03:41
%S 1,3,15,28,255,744,1209,2418,20440,65535,548856,2835756,4059264,
%T 4451832,10890040,13192608,23001132,23746333,27474741,54949482,
%U 55385589,110771178,220174080,222850677,445701354,4294967295,16331433888,18377794080,94951936080
%N Numbers k such that sigma(phi(k)) == 0 (mod k).
%C 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.
%C 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.
%o (PARI) isok(n) = sigma(eulerphi(n)) % n == 0; \\ _Michel Marcus_, Nov 20 2013
%Y Cf. A018784.
%K nonn
%O 1,2
%A _Benoit Cloitre_, Feb 18 2002
%E Edited by _Dean Hickerson_, Feb 20 2002
%E More terms from Sam Handler (sam_5_5_5_0(AT)yahoo.com), Nov 28 2004
%E a(26)-a(28) from _Donovan Johnson_, Jul 06 2012
%E a(29) from _Donovan Johnson_, Nov 27 2013