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Cubes of squarefree numbers.
24

%I #60 Sep 11 2024 23:47:38

%S 1,8,27,125,216,343,1000,1331,2197,2744,3375,4913,6859,9261,10648,

%T 12167,17576,24389,27000,29791,35937,39304,42875,50653,54872,59319,

%U 68921,74088,79507,97336,103823,132651,148877,166375,185193,195112,205379,226981,238328

%N Cubes of squarefree numbers.

%C Cubefull numbers (A036966) all of whose nonunitary divisors are not cubefull (A362147). - _Amiram Eldar_, May 13 2023

%H Vincenzo Librandi and T. D. Noe, <a href="/A062838/b062838.txt">Table of n, a(n) for n = 1..1000</a>

%F A055229(a(n)) = A005117(n) and A055229(m) < A005117(n) for m < a(n). - _Reinhard Zumkeller_, Apr 09 2010

%F a(n) = A005117(n)^3. - _R. J. Mathar_, Dec 03 2015

%F {a(n)} = {A225546(A000400(n)) : n >= 0}, where {a(n)} denotes the set of integers in the sequence. - _Peter Munn_, Oct 31 2019

%F Sum_{n>=1} 1/a(n) = zeta(3)/zeta(6) = 945*zeta(3)/Pi^6 (A157289). - _Amiram Eldar_, May 22 2020

%t Select[Range[70], SquareFreeQ]^3 (* _Harvey P. Dale_, Jul 20 2011 *)

%o (PARI) for(n=1,35, if(issquarefree(n),print(n*n^2)))

%o (PARI) a(n) = my(m, c); if(n<=1, n==1, c=1; m=1; while(c<n, m++; if(issquarefree(m), c++)); m^3); \\ _Altug Alkan_, Dec 03 2015

%o (Python)

%o from math import isqrt

%o from sympy import mobius

%o def A062838(n):

%o def f(x): return n+x-sum(mobius(k)*(x//k**2) for k in range(1, isqrt(x)+1))

%o m, k = n, f(n)

%o while m != k: m, k = k, f(k)

%o return m**3 # _Chai Wah Wu_, Sep 11 2024

%Y Other powers of squarefree numbers: A005117(1), A062503(2), A113849(4), A072774(all).

%Y Cf. A000400, A036966, A225546, A362147.

%Y A329332 column 3 in ascending order.

%K nonn,easy

%O 1,2

%A _Jason Earls_, Jul 21 2001

%E More terms from _Dean Hickerson_, Jul 24 2001

%E More terms from _Vladimir Joseph Stephan Orlovsky_, Aug 15 2008