OFFSET
1,1
COMMENTS
The asymptotic density of this sequence is (7/3) * Product_{p prime} (1 - 3/p^2) = (7/3) * A206256 = 0.292802955446... (Tsang, 1985). - Amiram Eldar, Feb 26 2024
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Kai-Man Tsang, The distribution of r-tuples of square-free numbers, Mathematika, Vol. 32, No. 2 (1985), pp. 265-275.
MATHEMATICA
Select[Range[200], AllTrue[{#, 2#+1, 3#+1}, SquareFreeQ]&] (* Harvey P. Dale, Oct 20 2014 *)
PROG
(PARI) j=[]; for(n=1, 200, if(issquarefree(n) && issquarefree(2*n+1) && issquarefree(3*n+1), j=concat(j, n))); j
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, Jul 21 2001
STATUS
approved