A081218 Greatest squarefree number not exceeding n-th prime power which is not prime.

1, 3, 7, 7, 15, 23, 26, 31, 47, 62, 79, 119, 123, 127, 167, 241, 255, 287, 341, 359, 511, 527, 623, 727, 839, 959, 1023, 1330, 1367, 1679, 1847, 2047, 2186, 2195, 2207, 2399, 2807, 3122, 3478, 3719, 4094, 4487, 4911, 5039, 5327, 6239, 6559, 6857, 6887, 7919

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Formula

a(n) = A070321(A025475(n)).

Mathematica

f[n_] := Module[{k = n-1}, While[!SquareFreeQ[k], k--]; k]; Join[{1}, f /@ Select[Range[8000], CompositeQ[#] && PrimePowerQ[#] &]] (* Amiram Eldar, Mar 26 2025 *)

Crossrefs

Cf. A025475, A070321, A081217.

Sequence in context: A393188 A059478 A175329 * A240422 A130003 A098581

Adjacent sequences: A081215 A081216 A081217 * A081219 A081220 A081221

Keyword

nonn

Author

Reinhard Zumkeller, Mar 10 2003

Status

approved