OFFSET
1,2
COMMENTS
The sequence differs from A098550 from a(11) onward.
The sequence is a permutation of the natural numbers. The proof is similar to that for A098550 (with minor changes). - Vladimir Shevelev, Jan 14 2015
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
David L. Applegate, Hans Havermann, Bob Selcoe, Vladimir Shevelev, N. J. A. Sloane, and Reinhard Zumkeller, The Yellowstone Permutation, arXiv preprint arXiv:1501.01669, 2015.
MAPLE
for n from 1 to 3 do
a[n]:= n:
b[n]:= 1:
od:
for n from 4 to 1000 do
q:= a[n-2]*a[n-3];
for k from 4 do
if not assigned(b[k]) and igcd(k, q) > 1 and igcd(k, a[n-1]) = 1 then
a[n]:= k;
b[k]:= 1;
break
fi
od:
od:
seq(a[i], i=1..1000); # Robert Israel, Jan 12 2015
MATHEMATICA
a[n_ /; n <= 3] := n; a[n_] := a[n] = For[aa = Table[a[j], {j, 1, n-1}]; k=4, True, k++, If[FreeQ[aa, k] && !CoprimeQ[k, a[n-2]*a[n-3]] && CoprimeQ[k, a[n-1]], Return[k]]]; Table[a[n], {n, 1, 60}] (* Jean-François Alcover, Jan 12 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jan 11 2015
EXTENSIONS
More terms from Jean-François Alcover, Jan 12 2015
STATUS
approved