The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A318169 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A318169

Composite numbers k such that sigma_2(k) - 1 is a square, where sigma_2(k) = A001157(k) is the sum of squares of divisors of k.
(history; published version)

#28 by Amiram Eldar at Wed Aug 07 13:01:42 EDT 2024

STATUS

reviewed

approved

#27 by Stefano Spezia at Wed Aug 07 12:59:11 EDT 2024

STATUS

proposed

reviewed

Discussion

Wed Aug 07

13:01

Amiram Eldar: Thanks.

#26 by Mamuka Jibladze at Wed Aug 07 12:55:04 EDT 2024

STATUS

editing

proposed

#25 by Mamuka Jibladze at Wed Aug 07 12:54:58 EDT 2024

COMMENTS

The values of sqrt(sigma_2(a(n))-1)) are 7, 47, 157, 3107, 3863, 54243, 257843, 6349657, 2207848187.

STATUS

approved

editing

#24 by Charles R Greathouse IV at Thu Sep 08 08:46:22 EDT 2022

PROG

(MAGMAMagma) [n: n in [2..6*10^6] |not IsPrime(n) and IsSquare(DivisorSigma(2, n)-1)]; // Vincenzo Librandi, Aug 22 2018

Discussion

Thu Sep 08

08:46

OEIS Server: https://oeis.org/edit/global/2944

#23 by Giovanni Resta at Wed Aug 22 10:02:27 EDT 2018

STATUS

reviewed

approved

#22 by Michel Marcus at Wed Aug 22 09:55:19 EDT 2018

STATUS

proposed

reviewed

#21 by Altug Alkan at Wed Aug 22 08:41:15 EDT 2018

STATUS

editing

proposed

#20 by Altug Alkan at Wed Aug 22 08:40:55 EDT 2018

CROSSREFS

Cf. A001157, A046655, A289290.

STATUS

proposed

editing

#19 by Altug Alkan at Wed Aug 22 08:34:21 EDT 2018

STATUS

editing

proposed