OFFSET
1,2
COMMENTS
Squarefree numbers coprime to 5.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) ~ Pi^2*n/5. - Charles R Greathouse IV, Sep 06 2016 [corrected by Amiram Eldar, Sep 26 2023]
Sum_{n>=1} 1/a(n)^s = (5^s)*zeta(s)/((1+5^s)*zeta(2*s)), s>1. - Amiram Eldar, Sep 26 2023
EXAMPLE
6 is in this sequence because 5*6 = 30 = 2*3*5 is squarefree.
MATHEMATICA
Select[Range[135], !Divisible[#, 5] && SquareFreeQ[#] &] (* Amiram Eldar, Sep 26 2023 *)
PROG
(Magma) [n: n in [1..135] | IsSquarefree(5*n)];
(PARI) lista(nn) = for(n=1, nn, if(issquarefree(5*n), print1(n, ", "))); \\ Altug Alkan, Sep 05 2016
(PARI) is(n)=n%5 && issquarefree(n) \\ Charles R Greathouse IV, Sep 06 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Juri-Stepan Gerasimov, Sep 05 2016
STATUS
approved