The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A113468 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A113468

Least number k such that k, k+n, k+2*n and k+3*n have the same number of divisors.
(history; published version)

#11 by OEIS Server at Sun Aug 04 03:00:24 EDT 2024

LINKS

Amiram Eldar, <a href="/A113468/b113468_1.txt">Table of n, a(n) for n = 1..10000</a>

#10 by Michel Marcus at Sun Aug 04 03:00:24 EDT 2024

STATUS

reviewed

approved

Discussion

Sun Aug 04

03:00

OEIS Server: Installed first b-file as b113468.txt.

#9 by Joerg Arndt at Sun Aug 04 02:42:53 EDT 2024

STATUS

proposed

reviewed

#8 by Amiram Eldar at Sun Aug 04 02:09:06 EDT 2024

STATUS

editing

proposed

#7 by Amiram Eldar at Sun Aug 04 01:50:29 EDT 2024

EXAMPLE

a(19) = 8 because 8, 8 + 19 = 27, 8 + 2*19 = 46 and 8 + 3*19 = 65 each have 4 divisors.

#6 by Amiram Eldar at Sun Aug 04 01:49:49 EDT 2024

MATHEMATICA

a[n_] := Module[{k = 1, d}, While[(d = DivisorSigma[0, k]) != DivisorSigma[0, k+n] || DivisorSigma[0, k+2*n] != d || DivisorSigma[0, k+3*n] != d, k++]; k]; Array[a, 60] (* Amiram Eldar, Aug 04 2024 *)

PROG

(PARI) a(n) = {my(k = 1, d); while((d = numdiv(k)) != numdiv(k+n) || numdiv(k+2*n) != d || numdiv(k+3*n) != d, k++); k; } \\ Amiram Eldar, Aug 04 2024

#5 by Amiram Eldar at Sun Aug 04 01:49:18 EDT 2024

NAME

Least number k such that n, k, k+n+, k, +2*n+2k and k+3*n+3k have the same number of divisors.

EXTENSIONS

Name corrected by Amiram Eldar, Aug 04 2024

#4 by Amiram Eldar at Sun Aug 04 01:46:57 EDT 2024

LINKS

Amiram Eldar, <a href="/A113468/b113468_1.txt">Table of n, a(n) for n = 1..10000</a>

STATUS

approved

editing

#3 by Russ Cox at Fri Mar 30 17:38:08 EDT 2012

AUTHOR

_David Wasserman (dwasserm(AT)earthlink.net), _, Jan 08 2006

Discussion

Fri Mar 30

17:38

OEIS Server: https://oeis.org/edit/global/184

#2 by N. J. A. Sloane at Fri Feb 27 03:00:00 EST 2009

NAME

Least k such that n, n+k, n+2k, and n+3k have the same number of divisors.

EXAMPLE

a(19) = 8 because 8, 27, 46, and 65 each have 4 divisors.

KEYWORD

nonn,new

nonn