A118016 - OEIS

%I #22 Sep 28 2024 21:02:19

%S 4,4,8,64,8192,268435456,576460752303423488,

%T 5316911983139663491615228241121378304,

%U 904625697166532776746648320380374280103671755200316906558262375061821325312

%N Integers of the form 2^k/(k-1).

%F a(n) = 4*A016031(n). - _Paolo P. Lava_, Nov 10 2006

%e k=5: 2^5/(5-1) = 32/4 = 8.

%e k=17: 2^17/(17-1) = 131072/16 = 8192.

%p P:=proc(n) local i,j; for i from 2 by 1 to n do j:=2^i/(i-1); if trunc(j)=j then print(j); fi; od; end: P(5000);

%t f[n_]:=2^n/n*2;Select[Table[f[n],{n,4,6!}],IntegerQ] (* _Vladimir Joseph Stephan Orlovsky_, Dec 05 2009 *)

%t Select[Table[2^n/(n-1),{n,2,500}],IntegerQ] (* _Harvey P. Dale_, Sep 27 2024 *)

%Y Cf. A016031 (de Bruijn's sequence: 2^(2^(n-1) - n)).

%K nonn

%O 1,1

%A _Paolo P. Lava_ and _Giorgio Balzarotti_, May 11 2006