OFFSET
1,1
COMMENTS
The asymptotic density of this sequence is 1 - (3/2)*A065474 = 0.5160488515... (Granville and Ramaré, 1996). - Amiram Eldar, Mar 02 2021
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Andrew Granville and Olivier Ramaré, Explicit bounds on exponential sums and the scarcity of squarefree binomial coefficients, Mathematika, Vol. 43, No. 1 (1996), pp. 73-107; alternative link.
MATHEMATICA
Select[Range[200], !SquareFreeQ[#(#+1)/2]&] (* Vladimir Joseph Stephan Orlovsky, Mar 30 2011 *)
PROG
(PARI) isok(k) = !issquarefree(k*(k+1)/2); \\ Michel Marcus, Feb 17 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Feb 19 2002
STATUS
approved