A068624 a(1) = 9; a(n+1) = smallest triangular number > a(n) formed by adding at least one digit to a(n).

9, 91, 1891, 18915, 1989015, 199890015, 19998900015, 1999989000015, 199999890000015, 19999998900000015, 1999999989000000015, 199999999890000000015, 19999999998900000000015

Offset

1,1

Links

Table of n, a(n) for n=1..13.

Formula

For n>=4, a(n) = 2*10^(2n-4) - 11*10^(n-2) + 15 [From Max Alekseyev, Apr 25 2009]

Crossrefs

Cf. A068618, A068619, A068621, A068622, A068623.

Sequence in context: A123792 A022520 A020236 * A034666 A022505 A225162

Adjacent sequences: A068621 A068622 A068623 * A068625 A068626 A068627

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