

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
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


LINKS

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


FORMULA

For n>=4, a(n) = 2*10^(2n4)  11*10^(n2) + 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



