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a(n) = floor( tan(n)^2 ).
7

%I #26 Feb 28 2024 08:08:10

%S 0,2,4,0,1,11,0,0,46,0,0,51053,0,0,52,0,0,12,1,0,5,2,0,2,4,0,1,10,0,0,

%T 41,0,0,5672,0,0,60,0,0,13,1,0,5,2,0,2,4,0,1,10,0,0,36,0,0,2041,0,0,

%U 69,0,0,14,1,0,5,2,0,2,4,0,1,9,0,0,32,0,0,1041,0,0,81,0,0,15,1,0,5,2,0,2,3,0,1,8,0,0,29,0,0,629

%N a(n) = floor( tan(n)^2 ).

%H Robert Israel, <a href="/A005657/b005657.txt">Table of n, a(n) for n = 0..10000</a>

%H R. K. Guy & N. J. A. Sloane, <a href="/A005648/a005648.pdf">Correspondence, 1985</a>

%F a(n) = A005699(n)-1 for n >= 1.

%p seq(floor(tan(n)^2),n=0..1000); # _Robert Israel_, Jun 14 2015

%t Floor[Tan[Range[0,70]]^2] (* _Harvey P. Dale_, Nov 06 2011 *)

%o (PARI) vector(100, n, n--; floor(tan(n)^2)) \\ _Michel Marcus_, Jun 15 2015

%o (Magma) [Floor(Tan(n)^2): n in [0..100]]; // _Vincenzo Librandi_, Jun 15 2015

%Y Cf. A000503, A005699.

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_