login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A076496 Numbers n such that sigma(n) == 12 (mod n). 10
1, 24, 30, 42, 54, 66, 78, 102, 114, 121, 138, 174, 186, 222, 246, 258, 282, 304, 318, 354, 366, 402, 426, 438, 474, 498, 534, 582, 606, 618, 642, 654, 678, 762, 780, 786, 822, 834, 894, 906, 942, 978, 1002, 1038, 1074, 1086, 1146, 1158, 1182, 1194, 1266, 1338 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

These numbers are also solutions of the equation: g[n]:=2n+1-sigma[n]=-11 (or they are cofacient numbers of type -11). - Vassil K. Tintschev (tinchev(AT)sunhe.jinr.ru), Dec 15 2004

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

EXAMPLE

6p is a solution if p>3 is prime, since sigma[6p]=1+2+3+6+p+2p+3p+6p=12(p+1)=2.6p+12=2n+12. These are "regular" solutions. Also n=121,304 are "singular" solutions. See other remainders in cross-references.

MATHEMATICA

Do[s=Mod[DivisorSigma[1, n], n]; If[IntegerQ[n/1000000], Print[{n}]]; If[Equal[s, 12], Print[{n, n/6}]], {n, 1, 1000}]

Join[{1}, Select[Range[2000], Mod[DivisorSigma[1, #], #]==12 &]] (* Vincenzo Librandi, Mar 11 2014 *)

PROG

(PARI) is(n)=sigma(n)%n==12 \\ Charles R Greathouse IV, Mar 09 2014

CROSSREFS

Cf. A054024, A045768, A045769, A045770, A076495, A076496, A088834.

Sequence in context: A030626 A302571 A125639 * A125640 A141545 A106682

Adjacent sequences:  A076493 A076494 A076495 * A076497 A076498 A076499

KEYWORD

nonn

AUTHOR

Labos Elemer, Oct 21 2002

EXTENSIONS

Initial term 1 added by Vincenzo Librandi, Mar 11 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 21 08:53 EDT 2019. Contains 323441 sequences. (Running on oeis4.)