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A272191 Either 8th power of a prime, or product of a square and a cube of two different primes. 1
72, 108, 200, 256, 392, 500, 675, 968, 1125, 1323, 1352, 1372, 2312, 2888, 3087, 3267, 4232, 4563, 5324, 6125, 6561, 6728, 7688, 7803, 8575, 8788, 9747, 10952, 11979, 13448, 14283, 14792, 15125, 17672, 19652, 19773, 21125, 22472, 22707, 25947, 27436, 27848, 29768 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers such that the sum of the number of divisors of their aliquot parts is four times the number of their divisors.

LINKS

Table of n, a(n) for n=1..43.

EXAMPLE

72 = 2^3 * 3^2;  256 = 2^8.

MAPLE

with(numtheory): P:=proc(q) local a, k, n;  for n from 2 to q do a:=sort([op(divisors(n))]);

if 4*tau(n)= add(tau(a[k]), k=1..nops(a)-1) then print(n); fi; od; end: P(10^7);

PROG

(PARI) isok(n) = 4*numdiv(n) == sumdiv(n, d, (n!=d)*numdiv(d)); \\ Michel Marcus, Apr 22 2016

CROSSREFS

Cf. A030516, A143610, A179645, A272190.

Sequence in context: A216426 A308053 A307758 * A072412 A052486 A114128

Adjacent sequences:  A272188 A272189 A272190 * A272192 A272193 A272194

KEYWORD

nonn,easy

AUTHOR

Paolo P. Lava, Apr 22 2016

STATUS

approved

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Last modified May 15 04:03 EDT 2021. Contains 343909 sequences. (Running on oeis4.)