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).

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

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..5000 (terms 1..100 from Paolo P. Lava)

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: A335288 A122839 A353869 * A121556 A123041 A078557

Adjacent sequences: A258074 A258075 A258076 * A258078 A258079 A258080

Keyword

nonn

Author

Paolo P. Lava, May 19 2015

Status

approved