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A258077 Numbers x such that (-1)sigma(x) | sigma(x), where (-1)sigma(x) is defined in A049060 and sigma(x) is the sum of the divisors of x (A000203). 2
1, 2, 3, 6, 14, 15, 30, 35, 42, 70, 78, 105, 190, 210, 348, 357, 418, 570, 714, 812, 910, 1045, 1254, 2090, 2436, 2730, 3135, 4060, 4522, 4674, 5278, 6270, 9990, 10659, 12180, 12441, 13566, 14630, 15834, 16770, 20026, 21318, 21978, 23374, 24244, 24871, 24882 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Paolo P. Lava, Table of n, a(n) for n = 1..100

EXAMPLE

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

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

(-1)sigma(35) = 24, sigma(35) = 48 and 48 / 24 = 2; 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)/b, integer) then print(n); fi; od; end: P(10^6);

CROSSREFS

Cf. A000203, A049060, A258079.

Sequence in context: A134737 A030733 A122839 * A121556 A123041 A078557

Adjacent sequences:  A258074 A258075 A258076 * A258078 A258079 A258080

KEYWORD

nonn

AUTHOR

Paolo P. Lava, May 19 2015

STATUS

approved

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Last modified December 12 07:03 EST 2018. Contains 318052 sequences. (Running on oeis4.)