OFFSET
1,2
COMMENTS
The asymptotic density of this sequence is (3/2)*A065474 = 0.4839511484... (Erdős and Ivić, 1987). - Amiram Eldar, Mar 02 2021
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
Paul Erdős and Aleksandar Ivić, The distribution of values of a certain class of arithmetic functions at consecutive integers, Colloq. Math. Soc. János Bolyai, Vol. 51 (1987), pp. 45-91.
FORMULA
a(n) = (A117203(n) - 1)/2.
EXAMPLE
10 and 2*10 +1 = 21 are both squarefree, so 10 is in the sequence.
MATHEMATICA
sfQ[n_]:=SquareFreeQ[n]&&SquareFreeQ[2n+1]; Select [Range[200], sfQ] (* Harvey P. Dale, Mar 12 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Mar 02 2006
EXTENSIONS
More terms from Jonathan Vos Post, Mar 03 2006
Corrected and extended by Harvey P. Dale, Mar 12 2011
STATUS
approved