

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
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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



