A379648 a(n) = position of prime(n) in A379652, or a(n) = -1 if prime(n) is not in A379652.

1, 7, 2, 8, 3, 13, 11, 6, 4, 17, 9, 14, 26, 49, 5, 47, 18, 154, 29, 12, 44, 46, 27, 120, 33, 16, 102, 48, 43, 36, 10, 87, 21, 52, 41, 15, 71, 86, 28, 58, 121, 31, 114, 172, 45, 190, 89, 189, 37, 108, 150, 19, 230, 83, 247, 88, 146, 30, 103, 74, 149, 59, 55, 119

Offset: 1

Author

Michael De Vlieger, Jan 01 2025

Keywords

• nonn
• easy

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A379652.

Programs

Mathematica

c[_] := True; j = 2; c[2] = False; r = 0; a[1] = PrimePi[j];
Do[m = 2*j + 1;
  While[
    Set[k, SelectFirst[FactorInteger[m][[All, 1]], c]]; ! IntegerQ[k],
    m = 2*m + 1];
  c[k] = False; j = k; a[PrimePi[k]] = n;
  If[k > r, r = k], {n, 2, 256}];
TakeWhile[Array[a, PrimePi[r]], IntegerQ]