The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A286884 Odd numbers k such that the set of distinct prime divisors of k is equal to the set of distinct prime divisors of the sum of proper divisors of k. 0
 108927, 448335, 544635, 53781261243, 92526188391, 612887145325 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The first four terms that are divisible by 108927 are 108927, 544635, 92526188391, 4094089374375. a(7) > 10^12. 2981095241355 is also a term. - Giovanni Resta, Aug 03 2017 LINKS EXAMPLE 92526188391 is a term because sigma(92526188391) - 92526188391 = 3^2*7*13^3*19*181^2 and 92526188391 = 3^2*7^2*13^2*19^3*181. MATHEMATICA fQ[n_] := Transpose[ FactorInteger[ n]][[1]] == Transpose[ FactorInteger[ DivisorSigma[1, n] - n]][[1]]; (* Robert G. Wilson v, Aug 02 2017 *) PROG (PARI) a001065(n) = if(n==0, 0, sigma(n) - n) a027748(n) = factor(n)[, 1]~ is(n) = n%2==1 && a027748(n)==a027748(a001065(n)) \\ Felix Fröhlich, Aug 02 2017 (PARI) list(lim)=my(v=List(), f, t, o); forfactored(n=108927, lim\1, f=n[2]; if(f[1, 1]==2, next); t=sigma(f)-n[1]; for(i=1, #f~, o=valuation(t, f[i, 1]); if(o==0, next(2)); t/=f[i, 1]^o); if(t==1, listput(v, n[1]))); Vec(v) \\ Charles R Greathouse IV, Aug 02 2017 CROSSREFS Cf. A001065, A007947, A027598, A027748, A286876. Sequence in context: A237789 A157533 A233650 * A210083 A238044 A237963 Adjacent sequences: A286881 A286882 A286883 * A286885 A286886 A286887 KEYWORD nonn,more AUTHOR Altug Alkan, Aug 02 2017 EXTENSIONS a(4)-a(6) from Giovanni Resta, Aug 03 2017 STATUS approved

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

Last modified February 8 07:51 EST 2023. Contains 360136 sequences. (Running on oeis4.)