login
A068624
a(1) = 9; a(n+1) = smallest triangular number > a(n) formed by adding at least one digit to a(n).
4
9, 91, 1891, 18915, 1989015, 199890015, 19998900015, 1999989000015, 199999890000015, 19999998900000015, 1999999989000000015, 199999999890000000015, 19999999998900000000015
OFFSET
1,1
FORMULA
For n>=4, a(n) = 2*10^(2n-4) - 11*10^(n-2) + 15 [From Max Alekseyev, Apr 25 2009]
CROSSREFS
KEYWORD
base,more,nonn
AUTHOR
Amarnath Murthy, Feb 25 2002
EXTENSIONS
3 more terms from Ray G. Opao, Dec 09 2004
Extended by Max Alekseyev, Apr 25 2009
STATUS
approved