OFFSET
1,2
COMMENTS
Complement of A067874 - R. J. Mathar, Feb 13 2010
The asymptotic density of this sequence is 1 - Product_{p prime} (1 - 2/p^2) = 0.677365... (1 - A065474). - Amiram Eldar, Feb 25 2021
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
5 is a term since 5^2-1 = 24 = 2^3*3 is not squarefree.
MATHEMATICA
f[n_]:=SquareFreeQ[n]; lst={}; Do[If[f[n^2-1], AppendTo[lst, n]], {n, 6!}]; lst
Select[Range[120], !SquareFreeQ[#^2-1]&] (* Harvey P. Dale, Jul 16 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Feb 12 2010
EXTENSIONS
Definition edited by R. J. Mathar, Feb 13 2010
STATUS
approved