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%I #16 Dec 12 2018 03:17:09
%S 0,0,0,3,1,2,1,0,0,1,3,1,1,3,1,1,1,1,0,1,1,3,0,0,0,2,1,0,1,0,1,2,1,2,
%T 0,0,2,0,0,1,2,1,1,0,0,0,4,3,2,2,2,0,0,4,5,1,2,1,1,2,0,1,0,1,0,0,0,2,
%U 0,0,1,1,2,1,2,1,0,1,2,2,4,4,1,0,0,1,1
%N a(n) is the number of even A098550 terms less than 2*prime(n) but occurring after 2*prime(n).
%H Peter J. C. Moses, <a href="/A255615/b255615.txt">Table of n, a(n) for n = 1..1000</a>
%H David L. Applegate, Hans Havermann, Bob Selcoe, Vladimir Shevelev, N. J. A. Sloane, and Reinhard Zumkeller, <a href="http://arxiv.org/abs/1501.01669">The Yellowstone Permutation</a>, arXiv preprint arXiv:1501.01669 [math.NT], 2015.
%e Let A=A098550. Let n=4, prime(4)=7, 2*prime(4)=14 = A(8). We have 2=A(2), 4=A(4), 6=A(10), 8=A(6), 10=A(16), 12=A(12). Thus 6,10 and 12 appear in A later than 14. So a(4)=3.
%t terms = 87;
%t f[lst_] := Block[{k = 4}, While[ GCD[ lst[[-2]], k] == 1 || GCD[ lst[[-1]], k] > 1 || MemberQ[lst, k], k++]; Append[lst, k]]; A098550 = Nest[f, {1, 2, 3}, 12 terms] ;
%t a[n_] := Module[{p, pos}, p = Prime[n]; pos = FirstPosition[A098550, 2 p][[1]]; Count[A098550[[pos+1 ;; 12 terms]], k_ /; EvenQ[k] && k < 2 p]];
%t Array[a, terms] (* _Jean-François Alcover_, Dec 12 2018, after _Robert G. Wilson v_ in A098550 *)
%Y Cf. A098550, A000040.
%K nonn
%O 1,4
%A _Vladimir Shevelev_, Feb 28 2015
%E More terms from _Peter J. C. Moses_, Feb 28 2015
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