login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A070015 Least m such that the sum of the aliquot parts of m (A001065) equals n, or 0 if no such number exists. 7
2, 0, 4, 9, 0, 6, 8, 10, 15, 14, 21, 121, 27, 22, 16, 12, 39, 289, 65, 34, 18, 20, 57, 529, 95, 46, 69, 28, 115, 841, 32, 58, 45, 62, 93, 24, 155, 1369, 217, 44, 63, 30, 50, 82, 123, 52, 129, 2209, 75, 40, 141, 0, 235, 42, 36, 106, 99, 68, 265, 3481, 371, 118, 64, 56 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Richard J. Mathar and Robert G. Wilson v, Table of n, a(n) for n = 1..10000 First 9884 from Richard J. Mathar.

Mersenne Forum, Given sigma(n)-n, find the smallest possible n

FORMULA

a(n) = min(x, A001065(x)=n) or a(n)=0 if n is an untouchable number (i.e., if from A005114).

EXAMPLE

n=128: a(n)=16129, divisors={1,127,16129}, 1+127=sigma[n]-n=128 and 16129 is the smallest.

MATHEMATICA

f[x_] := DivisorSigma[1, x]-x; t=Table[0, {128}]; Do[c=f[n]; If[c<129&&t[[c]]==0, t[[c]]=n], {n, 1000000}]; t

CROSSREFS

Cf. A000203, A001065, A048050, A051444, A007369, A070016, A005114, A048995.

Sequence in context: A101189 A001443 A195287 * A021492 A077119 A002938

Adjacent sequences:  A070012 A070013 A070014 * A070016 A070017 A070018

KEYWORD

nonn

AUTHOR

Labos Elemer, Apr 12 2002

STATUS

approved

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

Content is available under The OEIS End-User License Agreement .

Last modified December 19 02:47 EST 2014. Contains 252175 sequences.