A095864 Largest n-digit triangular number.

6, 91, 990, 9870, 99681, 998991, 9997156, 99991011, 999961560, 9999878910, 99999957291, 999999911791, 9999997965180, 99999998250180, 999999997764120, 9999999895728690, 99999999552805215, 999999998765257141

Offset: 1

Author

Ray Chandler, Jun 28 2004

Keywords

• base
• easy
• nonn

Comments

Triangular number with index given by A095863.

Crossrefs

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

Programs

Mathematica

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

Formula

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