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Revision History for A121878

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Showing entries 1-10 | older changes

A121878

a(1)=1. a(n) = the smallest positive integer not occurring earlier in the sequence such that a(n-1)+a(n) is squarefree.
(history; published version)

#20 by OEIS Server at Sun Jan 07 22:09:45 EST 2024

LINKS

Scott R. Shannon, <a href="/A121878/b121878_1.txt">Table of n, a(n) for n = 1..10000</a>

#19 by Michael De Vlieger at Sun Jan 07 22:09:45 EST 2024

STATUS

proposed

approved

Discussion

Sun Jan 07

22:09

OEIS Server: Installed first b-file as b121878.txt.

#18 by Scott R. Shannon at Sun Jan 07 19:58:23 EST 2024

STATUS

editing

proposed

#17 by Scott R. Shannon at Sun Jan 07 19:58:08 EST 2024

LINKS

Scott R. Shannon, <a href="/A121878/b121878_1.txt">Table of n, a(n) for n = 1..10000</a>

STATUS

approved

editing

Discussion

Sun Jan 07

19:58

Scott R. Shannon: Adding a bfile

#16 by Bruno Berselli at Wed Jun 03 17:23:57 EDT 2015

STATUS

proposed

approved

#15 by Michel Marcus at Tue Jun 02 00:29:05 EDT 2015

STATUS

editing

proposed

#14 by Michel Marcus at Tue Jun 02 00:29:00 EDT 2015

COMMENTS

Inverse: A167905; A167904(n) = a(a(n)). [From __Reinhard Zumkeller_, Nov 15 2009]

LINKS

<a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> [From __Reinhard Zumkeller_, Nov 15 2009]

MATHEMATICA

f[s_] := Block[{k = 1}, While[MemberQ[s, k] || Max @@ Last /@ FactorInteger[(s[[ -1]] + k)] > 1, k++ ]; Append[s, k]]; Nest[f, {1}, 75] (* _Ray Chandler_, Sep 06 2006 *)

CROSSREFS

Cf. A167907, A075380. [From __Reinhard Zumkeller_, Nov 15 2009]

STATUS

proposed

editing

#13 by Derek Orr at Mon Jun 01 22:22:22 EDT 2015

STATUS

editing

proposed

#12 by Derek Orr at Mon Jun 01 22:22:14 EDT 2015

COMMENTS

Conjectured to be a permutation of the natural numbers. - Derek Orr, Jun 01 2015

PROG

(PARI) v=[1]; n=1; while(n<100, if(issquarefree(v[#v]+n)&&!vecsearch(vecsort(v), n), v=concat(v, n); n=0); n++); v \\ Derek Orr, Jun 01 2015

STATUS

approved

editing

#11 by Charles R Greathouse IV at Wed Apr 09 10:15:52 EDT 2014

AUTHOR

Leroy Quet , Aug 31 2006

Discussion

Wed Apr 09

10:15

OEIS Server: https://oeis.org/edit/global/2152