A067144 Numbers k such that sigma(phi(k)) == 0 (mod k).

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

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