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A379649 a(0) = 1, a(n) = position of prime(n) in A379727, or a(n) = -1 if prime(n) is not in A379727.

%I A379649 #5 Jan 01 2025 01:49:07
%S A379649 1,-1,2,4,3,5,9,15,8,6,13,44,10,17,40,7,38,14,134,20,16,35,37,18,46,
%T A379649 24,12,153,39,34,27,45,71,104,43,32,11,95,70,19,82,47,22,165,98,36,
%U A379649 179,73,178,28,159,130,554,365,67,220,72,124,21,154,58,127,83,79
%N A379649 a(0) = 1, a(n) = position of prime(n) in A379727, or a(n) = -1 if prime(n) is not in A379727.
%C A379649 a(0) = 1 by definition to signify A379727(1) = 1.
%H A379649 Michael De Vlieger, <a href="/A379649/b379649.txt">Table of n, a(n) for n = 0..10000</a>
%t A379649 c[_] := True; j = 1; c[1] = False; r = 0; a[0] = 1;
%t A379649 Do[m = 2*j + 1;
%t A379649   While[
%t A379649     Set[k, SelectFirst[FactorInteger[m][[All, 1]], c]]; ! IntegerQ[k],
%t A379649     m = 2*m + 1];
%t A379649   c[k] = False; j = k; a[PrimePi[k]] = n;
%t A379649   If[k > r, r = k], {n, 2, 600}];
%t A379649 {1, -1}~Join~TakeWhile[Array[a, PrimePi[r] + 1, 2], IntegerQ]
%Y A379649 Cf. A379727.
%K A379649 sign,easy
%O A379649 0,3
%A A379649 _Michael De Vlieger_, Jan 01 2025