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

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A181597 (N\{4})-perfect numbers, i.e., numbers m for which sigma(m)-4 = 2m, if 4|m, otherwise sigma(m) = 2m. 2
 6, 12, 88, 1888, 32128, 521728, 1848964, 8378368, 34359083008, 549753192448 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Or union of {6}, near-perfect numbers m (cf. A181595) for which d(m)=4, and all odd perfect numbers (if they exist). Note that (N\{2})-perfect numbers are numbers for which sigma(m)-2=2m, if m is even, and sigma(m)=2m, if m is odd. They are all even numbers of A045768 and all odd perfect numbers (if they exist). LINKS EXAMPLE 88 is in the sequence since sigma(88) = 180 and 180 - 4 = 2*88. CROSSREFS Cf. A000396, A005101, A005820, A088832, A118372, A153501, A181595, A181596. Sequence in context: A054883 A005402 A128953 * A002898 A003613 A099767 Adjacent sequences: A181594 A181595 A181596 * A181598 A181599 A181600 KEYWORD nonn,more AUTHOR Vladimir Shevelev, Nov 01 2010, Nov 03 2010 EXTENSIONS Invalid term removed and a(8)-a(10) from Donovan Johnson, Sep 14 2013 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 December 5 14:51 EST 2022. Contains 358588 sequences. (Running on oeis4.)