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Revision History for A222208

(Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A222208

a(1) = 1, a(2) = 3; for n>2, a(n) = smallest number not in {a(1), ..., a(n-1)} such that a(n) is divisible by a(d) for all divisors d of n.
(history; published version)

#20 by Alois P. Heinz at Sun Jan 22 13:32:48 EST 2017

STATUS

reviewed

approved

#19 by Peter Luschny at Sun Jan 22 13:16:58 EST 2017

STATUS

proposed

reviewed

#18 by Jean-François Alcover at Sun Jan 22 11:09:30 EST 2017

STATUS

editing

proposed

#17 by Jean-François Alcover at Sun Jan 22 11:09:05 EST 2017

MATHEMATICA

a[1] = 1; a[2] = 3; a[n_] := a[n] = Module[{d, s, c, k}, d = Divisors[n] ~Complement~ {1, n}; For[s = Sort[Array[a, n-1]]; c = Complement[ Range[ Last[s]], s]; k = If[c == {}, Last[s]+1, First[c]], True, k++, If[FreeQ[s, k], If[AllTrue[d, Divisible[k, a[#]]&], Return[k]]]]];

Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Jan 22 2017 *)

STATUS

approved

editing

#16 by Reinhard Zumkeller at Wed Feb 13 18:02:45 EST 2013

STATUS

editing

approved

#15 by Reinhard Zumkeller at Wed Feb 13 15:11:34 EST 2013

PROG

(Haskell)

import Data.List (delete)

a222208 n = a222208_list !! (n-1)

a222208_list = 1 : 3 : f 3 (2 : [4 ..]) where

f u vs = g vs where

g (w:ws) = if all (== 0) $ map ((mod w) . a222208) $ a027751_row u

then w : f (u + 1) (delete w vs) else g ws

-- Reinhard Zumkeller, Feb 13 2013

CROSSREFS

Cf. A027751.

STATUS

approved

editing

#14 by Alois P. Heinz at Tue Feb 12 20:08:52 EST 2013

STATUS

editing

approved

#13 by Alois P. Heinz at Tue Feb 12 20:08:48 EST 2013

MAPLE

a:= proc(n) option remember; local h, i;

a:= proc(n) option remember; local h, i; if n<3 then h:= 2*n-1 else a(n-1); h:= ilcm(map(a,

#12 by Alois P. Heinz at Tue Feb 12 20:08:24 EST 2013

MAPLE

a:= proc(n) option remember; local h, i; if n<3 then h:= 2*n-1 else a(n-1); h:= ilcm(map(a,

h:= `if`(n<3, 2*n-1, ilcm(map(a,

numtheory[divisors](n) minus {1, n})[])) fi;

STATUS

approved

editing

#11 by Alois P. Heinz at Tue Feb 12 20:00:16 EST 2013

STATUS

editing

approved