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A070015 Least m such that the sum of the aliquot parts of m (A001065) equals n, or 0 if no such number exists. 8
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

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Last modified December 2 13:12 EST 2016. Contains 278678 sequences.