OFFSET
1,1
COMMENTS
a(n) = Product_{i=1..n} c(i), where c(i) is the difference between i and the next power of 10 (for example, c(13) = 100 - 13 = 87; c(100) = 1000 - 100 = 900). - Emeric Deutsch, Jul 31 2005
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..400
EXAMPLE
a(3) = (10-3)*(10-2)*(10-1) = 7*8*9 = 504.
MAPLE
s:=proc(m) nops(convert(m, base, 10)) end: for q from 1 to 120 do c[q]:=10^s(q)-q od: a:=n->product(c[i], i=1..n): seq(a(n), n=1..20); # Emeric Deutsch, Jul 31 2005
# second Maple program:
a:= proc(n) option remember; `if`(n=0, 1,
(10^length(n)-n)*a(n-1))
end:
seq(a(n), n=1..30); # Alois P. Heinz, Sep 22 2015
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Jul 29 2005
EXTENSIONS
More terms from Emeric Deutsch, Jul 31 2005
STATUS
approved