A258079 - OEIS

A258079

Numbers x such that (-1)sigma(x) | sigma(x) - x, where (-1)sigma(x) is defined in A049060 and sigma(x) - x is the sum of the aliquot parts of x (A001065).

1, 2, 6, 10, 36, 168, 1098, 1204, 2840, 19488, 1881124, 3105700, 445577184, 105314212224, 134633963520, 2167649138304

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OFFSET

1,2

COMMENTS

Ratio is equal to 1 for 2, 36, 1204, 2840, 1881124, 3105700, ...

a(17) > 10^13. - Hiroaki Yamanouchi, Sep 11 2015

LINKS

Table of n, a(n) for n=1..16.

EXAMPLE

(-1)sigma(1) = 1, sigma(1) - 1 = 1 - 1 = 0 and 0 / 1 = 0;

(-1)sigma(2) = 1, sigma(2) - 2 = 3 - 2 = 1 and 1 / 1 = 1;

(-1)sigma(36) = 55, sigma(36) - 36 = 91 - 36 = 55 and 55 / 55 = 1; etc.

MAPLE

with(numtheory): P:=proc(q) local a, b, i, j, n; for n from 1 to q do a:=ifactors(n)[2]:

b:=1; for i from 1 to nops(a) do b:=b*(-1+sum(a[i][1]^j, j=1..a[i][2])): od:

if type((sigma(n)-n)/b, integer) then print(n); fi; od; end: P(10^6);

CROSSREFS

Cf. A001065, A049060, A258077.

Sequence in context: A218965 A248821 A260559 * A027165 A111414 A308486

Adjacent sequences: A258076 A258077 A258078 * A258080 A258081 A258082

KEYWORD

nonn,more

AUTHOR

Paolo P. Lava, May 19 2015

EXTENSIONS

a(13)-a(16) from Hiroaki Yamanouchi, Sep 11 2015

STATUS

approved