The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A202160 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
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A202160

a(n) = smallest k having at least five prime divisors d such that (d + n) | (k + n).
(history; published version)

#25 by Joerg Arndt at Mon Sep 09 04:24:22 EDT 2019

STATUS

reviewed

approved

#24 by Michel Marcus at Mon Sep 09 03:50:47 EDT 2019

STATUS

proposed

reviewed

#23 by Amiram Eldar at Mon Sep 09 03:47:49 EDT 2019

STATUS

editing

proposed

#22 by Amiram Eldar at Mon Sep 09 03:37:24 EDT 2019

MATHEMATICA

numd[n_, k_] := Module[{p=FactorInteger[k][[;; , 1]], c=0}, Do[If[Divisible[n+k, n+p[[i]]], c++], {i, 1, Length[p]}]; c]; a[n_]:=Module[{k=1}, While[numd[n, k] <= 4, k++]; k]; Array[a, 30] (* Amiram Eldar, Sep 09 2019 *)

#21 by Amiram Eldar at Mon Sep 09 03:25:35 EDT 2019

LINKS

Amiram Eldar, <a href="/A202160/b202160.txt">Table of n, a(n) for n = 1..125</a>

STATUS

approved

editing

#20 by N. J. A. Sloane at Sat Sep 16 00:35:07 EDT 2017

STATUS

proposed

approved

#19 by Jon E. Schoenfield at Fri Sep 15 19:26:59 EDT 2017

STATUS

editing

proposed

#18 by Jon E. Schoenfield at Fri Sep 15 19:26:56 EDT 2017

COMMENTS

The sequence of numbers k composite and squarefree, prime p | k ==> p+n | k+n is given by A029591 (least quasi-Carmichael number of order -n).

STATUS

proposed

editing

#17 by Jon E. Schoenfield at Fri Sep 15 19:23:24 EDT 2017

STATUS

editing

proposed

#16 by Jon E. Schoenfield at Fri Sep 15 19:21:54 EDT 2017

COMMENTS

The sequence a(n) = of numbers k composite and squarefree, prime p | k ==> p+n | k+n is given by A029591 (least quasi-Carmichael number of order -n).

In this sequence, the majority of numbers terms are not squarefree.

EXAMPLE

a(3) = 460317 because the primes prime divisors of 460317 are 3, 11, 13, 29, 37 =>

STATUS

approved

editing

Discussion

Fri Sep 15

19:23

Jon E. Schoenfield: Unless I misunderstood what was there, the use of "a(n)" in the first sentence of the Comments section was an error.  Is my rewording okay?  Or have I misunderstood, and somehow it was okay as it was?