A156899 a(n) = the largest prime power <= the n-th positive squarefree integer.

1, 2, 3, 5, 5, 7, 9, 11, 13, 13, 13, 17, 19, 19, 19, 23, 25, 29, 29, 31, 32, 32, 32, 37, 37, 37, 41, 41, 43, 43, 47, 49, 53, 53, 53, 53, 59, 61, 61, 64, 64, 67, 67, 67, 71, 73, 73, 73, 73, 79, 81, 83, 83, 83, 83, 89, 89, 89, 89, 89, 97, 101, 101, 103, 103, 103, 107, 109, 109

Offset: 1

Author

Leroy Quet, Feb 17 2009

Keywords

• nonn

Comments

The first positive squarefree integer is considered to be 1 here.

Links

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

Crossrefs

Cf. A081217, A156898, A156900, A005117, A000961.

Programs

Mathematica

Block[{nn = 110, s}, s = Select[Range[nn], SquareFreeQ]; Map[If[# == 1, 1, SelectFirst[# - Range[0, # - 1], PrimePowerQ]] &, s]] (* Michael De Vlieger, Oct 30 2017 *)

Extensions

Extended by Ray Chandler, Jun 19 2009