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