The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A284724

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A284724

a(n) = (1/2) * smallest even number missing from [A280864(1), ..., A280864(n-1)].
(history; published version)

#27 by Alois P. Heinz at Thu Nov 23 19:42:19 EST 2017

STATUS

reviewed

approved

#26 by Joerg Arndt at Thu Nov 23 12:29:36 EST 2017

STATUS

proposed

reviewed

#25 by Jean-François Alcover at Thu Nov 23 12:27:22 EST 2017

STATUS

editing

proposed

#24 by Jean-François Alcover at Thu Nov 23 12:27:14 EST 2017

MATHEMATICA

terms = 80; rad[n_] := Times @@ FactorInteger[n][[All, 1]];

A280864 = Reap[present = 0; p = 1; pp = 1; Do[forbidden = GCD[p, pp]; mandatory = p/forbidden; a = mandatory; While[BitGet[present, a] > 0 || GCD[forbidden, a] > 1, a += mandatory]; Sow[a]; present += 2^a; pp = p; p = rad[a], terms]][[2, 1]];

Clear[a];

a[1] = 1;

a[n_] := a[n] = For[b = 2a[n-1], True, b += 2, If[FreeQ[A280864[[1 ;; n-1]], b], Return[b/2]]];

Array[a, terms] (* Jean-François Alcover, Nov 23 2017, after Rémy Sigrist program for A280864 *)

STATUS

approved

editing

#23 by N. J. A. Sloane at Fri Apr 07 21:33:37 EDT 2017

STATUS

editing

approved

#22 by N. J. A. Sloane at Fri Apr 07 21:33:35 EDT 2017

COMMENTS

For k>=2, 1, n>=1, let B_k(n) = smallest multiple of k missing from [A280864(1), ..., A280864(n-1)]. Sequence gives values of B_2(n)/2.

STATUS

proposed

editing

#21 by Rémy Sigrist at Fri Apr 07 17:10:51 EDT 2017

STATUS

editing

proposed

#20 by Rémy Sigrist at Fri Apr 07 17:08:08 EDT 2017

COMMENTS

For k>=2, n>=1, let B_k(n) = smallest even number multiple of k missing from [A280864(1), ..., A280864(n-1)]. Sequence gives values of B_2(n)/2.

Needs a b-file.

LINKS

Rémy Sigrist, <a href="/A284724/b284724.txt">Table of n, a(n) for n = 1..10000</a>

STATUS

approved

editing

#19 by N. J. A. Sloane at Thu Apr 06 22:53:53 EDT 2017

STATUS

editing

approved

#18 by N. J. A. Sloane at Thu Apr 06 22:53:51 EDT 2017

CROSSREFS

Cf. A280864, A064413, A284725, A284726.

STATUS

approved

editing