cp's OEIS Frontend

A361504 Index of n in A359804, or -1 if n never appears there.

%I A361504 #19 Mar 19 2023 21:12:31
%S A361504 1,2,3,5,4,6,8,10,9,7,13,14,42,12,11,24,347,19,3466,15,16,17,49012,25,
%T A361504 18,31,32,20,528231,21,717126,38,22,44,23,35,63056215,47,45,26,
%U A361504 1375559400,27,7038527851,28,29,55
%N A361504 Index of n in A359804, or -1 if n never appears there.
%C A361504 Conjectured to be a permutation of the natural numbers.
%t A361504 nn = 2^20; c[_] = 0; q[_] = 1;
%t A361504 Array[Set[{a[#], c[#]}, {#, #}] &, 2];
%t A361504 Set[{i, j}, {a[1], a[2]}]; u = 3;
%t A361504 Monitor[Do[
%t A361504   (k = q[#]; While[c[k #] > 0, k++]; k *= #;
%t A361504      While[c[# q[#]] > 0, q[#]++]) &[(p = 2;
%t A361504     While[Divisible[i j, p], p = NextPrime[p]]; p)]; Sow[p];
%t A361504   Set[{a[n], c[k], i, j}, {k, n, j, k}];
%t A361504   If[k == u, While[c[u] > 0, u++]], {n, 3, nn}], n];
%t A361504 TakeWhile[Array[c, 120], # > 0 &] (* _Michael De Vlieger_, Mar 18 2023 *)
%Y A361504 Cf. A359804, A361502.
%K A361504 nonn,more
%O A361504 1,2
%A A361504 _N. J. A. Sloane_, Mar 18 2023