OFFSET
1,2
FORMULA
Triangular number with index given by A068092.
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 *)
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Feb 19 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 06 2002
STATUS
approved