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!)
A037159 Consider the trajectory of n under the iteration of a map which sends x to 3x - sigma(x) if this is >= 0; otherwise the iteration stops. The sequence gives values of n which eventually reach 0. 4

%I #17 Jul 30 2020 15:09:39

%S 82,120,280,672,1464,3048,4964,5568,5688,7666,8969,9176,9288,9514,

%T 9616,9706,10132,10186,10232,10478,11496,11884,11914,12232,12320,

%U 12820,13248,13842,13854,13866,14848,15076,15098,15196,15364,15586,15892

%N Consider the trajectory of n under the iteration of a map which sends x to 3x - sigma(x) if this is >= 0; otherwise the iteration stops. The sequence gives values of n which eventually reach 0.

%C A perfect number is a fixed point of this map.

%e 82 -> 120 -> 0.

%t max = 16000; f[0] = 0; f[n_ /; 0 < n < 9max] := 3n - DivisorSigma[1, n]; f[_] = -1; Select[ Range[max], FixedPoint[f, #] == 0 &] (* _Jean-François Alcover_, Feb 22 2012 *)

%Y To see why 1, 16 and 23 are not in the sequence, see A058541, A058542 and A058545.

%Y Cf. A033885, A033945, A033946, A037160.

%K nonn,nice

%O 1,1

%A _Naohiro Nomoto_

%E Better description from _Jud McCranie_, Dec 24 2000

%E Definition clarified by _Harvey P. Dale_, Jul 30 2020

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 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)