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A095864 Largest n-digit triangular number. 7

%I #8 Jul 27 2012 18:50:36

%S 6,91,990,9870,99681,998991,9997156,99991011,999961560,9999878910,

%T 99999957291,999999911791,9999997965180,99999998250180,

%U 999999997764120,9999999895728690,99999999552805215,999999998765257141

%N Largest n-digit triangular number.

%C Triangular number with index given by A095863.

%F a(n) = A068093(n+1) - A068092(n+1).

%t Join[{6},(#(#+1))/2&/@Table[Floor[(Sqrt[8*10^n+1]-1)/2],{n,2,30}]] (* _Harvey P. Dale_, Jul 27 2012 *)

%t triInverse[n_] := Floor[(Sqrt[1 + 8*n] - 1)/2]; tri[n_] := n*(n+1)/2; Table[tri[triInverse[10^n - 1]], {n, 18}] (* _T. D. Noe_, Jul 27 2012 *)

%Y Cf. A068092, A068093, A068094, A095863, A095865, A095866.

%K base,easy,nonn

%O 1,1

%A _Ray Chandler_, Jun 28 2004

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Last modified March 28 08:22 EDT 2024. Contains 371236 sequences. (Running on oeis4.)