A344347 Numbers k such that sigma(k)^2 is divisible by k-1.

2, 3, 5, 10, 33, 55, 82, 129, 136, 145, 261, 351, 385, 406, 442, 513, 649, 897, 1090, 2241, 4726, 5185, 8650, 13601, 17101, 17641, 18241, 26625, 26937, 29697, 29953, 32896, 34561, 35841, 38417, 44955, 46081, 46593, 51985, 63505, 65703, 66249, 84376, 93313, 97903

Offset

1,1

Links

Table of n, a(n) for n=1..45.

Example

For k=10, sigma(10)^2 / (10-1) = 18^2 / 9 = 324 / 9 = 36.

Mathematica

Select[Range[2, 10^5], Divisible[DivisorSigma[1, #]^2, # - 1] &] (* Amiram Eldar, May 15 2021 *)

Prog

(PARI)
list(nn) = for(n=2, nn, if (sigma(n)^2 % (n-1) == 0, print1(n, ", ")))
list(100000)

Crossrefs

Cf. A072861, A263928.

Sequence in context: A003182 A348260 A363257 * A134294 A154956 A197312

Adjacent sequences: A344344 A344345 A344346 * A344348 A344349 A344350

Keyword

nonn

Author

Zdenek Cervenka, May 15 2021

Status

approved