OFFSET
1,2
EXAMPLE
After a(n)=1 we cannot have 10 (presence of a "0"), thus 11; product of 1x1 is 1, so next integer must contain a "1", thus 12; product 1x2=2, so next integer must contain a "2", thus 21 (20 not allowed), etc.
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Eric Angelini, Jun 09 2005
STATUS
approved