A068093 Smallest n-digit triangular number.

1, 10, 105, 1035, 10011, 100128, 1000405, 10001628, 100005153, 1000006281, 10000020331, 100000404505, 1000001326005, 10000002437316, 100000012392316, 1000000042485480, 10000000037150046, 100000000000018810, 1000000000179470703, 10000000002237948990

Offset: 1

Author

Amarnath Murthy, Feb 19 2002

Keywords

• base
• easy
• nonn

Crossrefs

Cf. A068092, A068094, A095863, A095864, A095865, A095866.

Programs

Mathematica

triInverse[n_] := Floor[(Sqrt[1 + 8*n] - 1)/2]; tri[n_] := n*(n+1)/2; Table[tri[1 + triInverse[10^(n-1) - 1]], {n, 20}] (* T. D. Noe, Jul 27 2012 *)

Formula

Triangular number with index given by A068092.

Extensions

More terms from Sascha Kurz, Mar 06 2002