A246699 - OEIS

%I #28 Sep 08 2022 08:46:09

%S 1,2,3,6,11,21,29,31,51,55,57

%N Squarefree n such that C(2^n - 1, n) is also squarefree, where C is the binomial coefficient.

%C Conjectured to be finite.

%C The subsequence of squarefree numbers in A245569. - _M. F. Hasler_, Nov 28 2014

%t Select[Range[100], SquareFreeQ[#] && SquareFreeQ[Binomial[2^# - 1, #]] &] (* _Vincenzo Librandi_, Nov 14 2014 *)

%o (Magma) [n: n in [1..200] | IsSquarefree(n) and IsSquarefree(Binomial(2^n-1, n))];

%o (PARI) is(n)=issquarefree(n) && issquarefree(binomial(2^n-1,n)) \\ _Charles R Greathouse IV_, Nov 16 2014

%Y Cf. A000225, A005117, A136556.

%K nonn

%O 1,2

%A _Juri-Stepan Gerasimov_, Nov 15 2014