The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A277273

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A277273

Numbers k such that sigma(k) = sigma(k - d(k)).
(history; published version)

#23 by Charles R Greathouse IV at Thu Sep 08 08:46:17 EDT 2022

PROG

(MAGMAMagma) [n: n in [3..50000] | DivisorSigma(1, n) eq DivisorSigma(1, n-DivisorSigma(0, n))]; // Vincenzo Librandi, Nov 21 2016

Discussion

Thu Sep 08

08:46

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

#22 by Bruno Berselli at Mon Nov 21 06:19:12 EST 2016

STATUS

reviewed

approved

#21 by Joerg Arndt at Mon Nov 21 06:03:52 EST 2016

STATUS

proposed

reviewed

#20 by Vincenzo Librandi at Mon Nov 21 01:54:16 EST 2016

STATUS

editing

proposed

#19 by Vincenzo Librandi at Mon Nov 21 01:54:04 EST 2016

PROG

(MAGMA) [n: n in [3..50000] | DivisorSigma(1, n) eq DivisorSigma(1, n-DivisorSigma(0, n))]; // Vincenzo Librandi, Nov 21 2016

STATUS

proposed

editing

#18 by Jon E. Schoenfield at Sun Nov 20 22:11:25 EST 2016

STATUS

editing

proposed

#17 by Jon E. Schoenfield at Sun Nov 20 22:11:23 EST 2016

COMMENTS

If p, p+2, 3p+2 and 3p+8 are primes, then (p+2)*(3p+2) is in the sequence. Dickson's conjecture implies that there are infinitely many such p. Terms of this form include 55, 119, 1007, 118007, 6120407, 8350007, 13083407, 51875207. - Robert Israel, Nov 20 2016

STATUS

proposed

editing

#16 by Robert Israel at Sun Nov 20 22:04:54 EST 2016

STATUS

editing

proposed

#15 by Robert Israel at Sun Nov 20 21:58:03 EST 2016

COMMENTS

#14 by Robert Israel at Sun Nov 20 21:29:44 EST 2016

LINKS

Robert Israel, <a href="/A277273/b277273.txt">Table of n, a(n) for n = 1..448</a>

MAPLE

select(n -> numtheory:-sigma(n) = numtheory:-sigma(n - numtheory:-tau(n)), [$2..10^5]); # Robert Israel, Nov 20 2016

STATUS

approved

editing