A264387 2*(1+2*a(n)) is the n-th even squarefree number A039956(n), n >= 1.

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

Offset: 1

Author

Wolfdieter Lang, Dec 23 2015

Keywords

• nonn
• easy

Comments

The asymptotic density of this sequence is 8/Pi^2 (A217739). - Amiram Eldar, Sep 26 2023

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A039956, A217739.

Programs

Mathematica

(# - 2)/4 & /@ Select[2 Range@ 202, SquareFreeQ] (* Michael De Vlieger, Dec 23 2015 *)

PARI

lista(max) = forstep(k = 2, 4*max+2, 2, if(issquarefree(k), print1((k-2)/4, ", "))); \\ Amiram Eldar, Sep 26 2023

Formula

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