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A081217 Greatest squarefree number not exceeding n-th prime power. 6
1, 2, 3, 3, 5, 7, 7, 7, 11, 13, 15, 17, 19, 23, 23, 26, 29, 31, 31, 37, 41, 43, 47, 47, 53, 59, 61, 62, 67, 71, 73, 79, 79, 83, 89, 97, 101, 103, 107, 109, 113, 119, 123, 127, 127, 131, 137, 139, 149, 151, 157, 163, 167, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = A070321(A000961(n)).

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

n:= 0:

for m from 1 while n <= 100 do

  if numtheory:-issqrfree(m) then s:= m fi;

  if nops(numtheory:-factorset(m)) <= 1 then n:= n+1; A[n]:= s fi

od:

seq(A[i], i=1..100); # Robert Israel, Jan 08 2018

MATHEMATICA

nmax = 100; coeff = 5;

A000961 = Join[{1}, Select[Range[2, coeff*nmax], PrimePowerQ]];

a070321[n_] := For[k = n, True, k--, If[SquareFreeQ[k], Return[k]]];

a[n_] := If[n > Length[A000961], Print["error: increase insufficient coeff ", coeff], a070321[A000961[[n]] ] ];

Array[a, nmax] (* Jean-Fran├žois Alcover, Mar 08 2019 *)

CROSSREFS

Cf. A081218.

Cf. A156898, A156899, A156900, A005117, A000961

Sequence in context: A231406 A214034 A047844 * A320036 A053271 A035360

Adjacent sequences:  A081214 A081215 A081216 * A081218 A081219 A081220

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 10 2003

STATUS

approved

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Last modified April 9 20:55 EDT 2020. Contains 333363 sequences. (Running on oeis4.)