The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A015819 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A015819

Numbers k such that phi(k + 3) | sigma(k).
(history; published version)

#30 by Alois P. Heinz at Thu Dec 13 12:48:33 EST 2018

STATUS

proposed

approved

#29 by Robert Israel at Thu Dec 13 11:35:01 EST 2018

STATUS

editing

proposed

#28 by Robert Israel at Thu Dec 13 11:34:53 EST 2018

MAPLE

select(t -> (numtheory:-sigma(t)/numtheory:-phi(t+3))::integer, [$1..1000]); # Robert Israel, Dec 13 2018

CROSSREFS

Contains A092109.

STATUS

proposed

editing

#27 by Michel Marcus at Thu Dec 13 00:55:03 EST 2018

STATUS

editing

proposed

#26 by Michel Marcus at Thu Dec 13 00:54:48 EST 2018

CROSSREFS

Cf. A056097.

STATUS

proposed

editing

#25 by Sean A. Irvine at Wed Dec 12 23:00:41 EST 2018

STATUS

editing

proposed

#24 by Sean A. Irvine at Wed Dec 12 23:00:34 EST 2018

PROG

(PARI) is(n)=sigma(n)%(eulerphi(n)+3))==0 \\ Charles R Greathouse IV, Sep 25 2012

STATUS

approved

editing

#23 by Joerg Arndt at Fri Aug 31 02:54:07 EDT 2018

STATUS

proposed

approved

#22 by Jon E. Schoenfield at Thu Aug 30 23:37:54 EDT 2018

STATUS

editing

proposed

#21 by Jon E. Schoenfield at Thu Aug 30 23:37:50 EDT 2018

NAME

Numbers n k such that phi(n k + 3) | sigma(nk).

MATHEMATICA

Select[Range[1000], Divisible[DivisorSigma[1, #], EulerPhi[3 + #]] &] (* _David Nacin, _, Mar 01 2012 *)

STATUS

approved

editing