A110396 - OEIS

%I #15 Mar 05 2019 20:44:17

%S 9,72,504,3024,15120,60480,181440,362880,362880,32659200,2906668800,

%T 255786854400,22253456332800,1913797244620800,162672765792768000,

%U 13664512326592512000,1134154523107178496000,93000670894788636672000,7533054342477879570432000

%N 10's complement factorial of n: a(n) = (10's complement of n)*(10's complement of n-1)*...*(10's complement of 2)*(10's complement of 1).

%C 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

%H Alois P. Heinz, <a href="/A110396/b110396.txt">Table of n, a(n) for n = 1..400</a>

%e a(3) = (10-3)*(10-2)*(10-1) = 7*8*9 = 504.

%p 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

%p # second Maple program:

%p a:= proc(n) option remember; `if`(n=0, 1,

%p        (10^length(n)-n)*a(n-1))

%p     end:

%p seq(a(n), n=1..30);  # _Alois P. Heinz_, Sep 22 2015

%Y Cf. A110394, A110395.

%K base,easy,nonn

%O 1,1

%A _Amarnath Murthy_, Jul 29 2005

%E More terms from _Emeric Deutsch_, Jul 31 2005