A053850 - OEIS

%I #29 Nov 21 2020 04:01:07

%S 9,25,27,45,49,63,75,81,99,117,121,125,135,147,153,169,171,175,189,

%T 207,225,243,245,261,275,279,289,297,315,325,333,343,351,361,363,369,

%U 375,387,405,423,425,441,459,475,477,495,507,513,525,529,531,539,549,567

%N Odd numbers divisible by a square > 1.

%C Odd n such that sum(k=1,n-1,floor(k^3/n)) is different from (1/4)*(n-2)*(n^2-1) (equality holds for n prime as well as for "1" union "A024556" ). - _Benoit Cloitre_, Dec 08 2002

%C Odd nonsquarefree numbers, odd terms of A013929. - _Zak Seidov_, Aug 16 2006

%C The asymptotic density of this sequence is 1/2 - 4/Pi^2 = 0.094715... - _Amiram Eldar_, Nov 21 2020

%H Amiram Eldar, <a href="/A053850/b053850.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/PrimeSums.html">Prime Sums</a>.

%t Select[Range[1, 500, 2], !SquareFreeQ[#] &] (* _Amiram Eldar_, Nov 21 2020 *)

%o (PARI) lista(nn) = {forstep(n=1, nn, 2, if (! issquarefree(n), print1(n, ", ")));} \\ _Michel Marcus_, Jun 06 2014

%Y Cf. A078837, A013929, A024556.

%K easy,nonn

%O 1,1

%A _Enoch Haga_, Mar 28 2000