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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A069085 Abundant numbers n such that n = sigma(k) - 2k, where k = sigma(n) - 2n. 4
 120, 672, 45840, 51168, 523776, 459818240, 1476304896, 51001180160 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All triply perfect numbers (A005820) are in the sequence, as are 45840 and 51168. Are there any other terms? a(8) > 10^10. - Donovan Johnson, Apr 22 2012 a(9) > 1.3*10^11. - Giovanni Resta, Jun 06 2016 LINKS Table of n, a(n) for n=1..8. EXAMPLE sigma(45840) - 2*45840 = 51168 and sigma(51168) - 2*51168 = 45840, so 45840 and 51168 are in the sequence. MATHEMATICA For[n=1, True, n++, k=DivisorSigma[1, n]-2n; If[k>0&&DivisorSigma[1, k]-2k==n, Print[n]]] CROSSREFS Cf. A005820. Sequence in context: A281771 A166069 A114887 * A039688 A005820 A306602 Adjacent sequences: A069082 A069083 A069084 * A069086 A069087 A069088 KEYWORD more,nonn AUTHOR Naohiro Nomoto, Apr 05 2002 EXTENSIONS Edited by Dean Hickerson, Apr 11 2002 a(7) from Donovan Johnson, Apr 22 2012 a(8) from Giovanni Resta, Jun 06 2016 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 July 19 22:34 EDT 2024. Contains 374441 sequences. (Running on oeis4.)