A264387 - OEIS

%I #18 Sep 26 2023 01:57:42

%S 0,1,2,3,5,6,7,8,9,10,11,14,15,16,17,18,19,20,21,23,25,26,27,28,29,30,

%T 32,33,34,35,36,38,39,41,42,43,44,45,46,47,48,50,51,52,53,54,55,56,57,

%U 59,61,63,64,65,66,68,69,70,71,72,74,75,77,78,79,80,81,82,83,86,88,89,90,91,92,93,95,96,97,98,99,100

%N 2*(1+2*a(n)) is the n-th even squarefree number A039956(n), n >= 1.

%C The asymptotic density of this sequence is 8/Pi^2 (A217739). - _Amiram Eldar_, Sep 26 2023

%H G. C. Greubel, <a href="/A264387/b264387.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = (A039956(n) - 2)/4, n >= 1.

%t (# - 2)/4 & /@ Select[2 Range@ 202, SquareFreeQ] (* _Michael De Vlieger_, Dec 23 2015 *)

%o (PARI) lista(max) = forstep(k = 2, 4*max+2, 2, if(issquarefree(k), print1((k-2)/4, ", "))); \\ _Amiram Eldar_, Sep 26 2023

%Y Cf. A039956, A217739.

%K nonn,easy

%O 1,3

%A _Wolfdieter Lang_, Dec 23 2015