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

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A322486 Semi-unitary perfect numbers: numbers k such that susigma(k) = 2k, where susigma(k) is the sum of the semi-unitary divisors of k (A322485). 5
6, 60, 90, 264, 3960, 4560, 8736, 13770, 131040, 384384, 605880, 5765760, 20049120, 882161280, 23253135360 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
a(16) <= 1846273228800. - David A. Corneth, Dec 11 2018
LINKS
EXAMPLE
264 is in the sequence since its sum of semi-unitary divisors is susigma(264) = 528 = 2 * 264.
MATHEMATICA
f[p_, e_] := (p^Floor[(e+1)/2] - 1)/(p-1) + p^e; susigma[n_] := If[n==1, 1, Times @@ (f @@@ FactorInteger[n])]; aQ[n_] := susigma[n]==2n; Select[Range[10000], aQ]
PROG
(PARI) ssu(n) = {my(f = factor(n)); for (k=1, #f~, my(p=f[k, 1], e=f[k, 2]); f[k, 1] = (p^((e+1)\2) - 1)/(p-1) + p^e; f[k, 2] = 1; ); factorback(f); } \\ A322485
isok(n) = ssu(n) == 2*n; \\ Michel Marcus, Dec 14 2018
CROSSREFS
Sequence in context: A189000 A007358 A334406 * A323757 A331108 A324707
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Dec 11 2018
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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)