%I A117644
%S A117644 4,45,369,2961,23697,189585,1516689
%N A117644 Number of different couples of different numbers, with digits different 
               from zero, that produce a sum equal to 10, 100, 1000, 10000, 100000, 
               1000000, etc.
%e A117644 Es. 10 = 1 + 9 = 2 + 8 = 3 + 7 = 4 + 6 therefore we have 4 different 
               couples
%e A117644 9 + 1 is not considered because is the same couple as 1 + 9
%e A117644 5 + 5 is not considered because we consider couples with different numbers
%p A117644 P:=proc(n)local i,j,k,ok,count; count:=0; for i from 1 by 1 to n/2-1 
               do ok:=0; k:=i; while k>0 do j:=frac(k/10)*10; if j=0 then ok:=1; 
               fi; k:=trunc(k/10); od; k:=n-i; while k>0 do j:=frac(k/10)*10; if 
               j=0 then ok:=1; fi; k:=trunc(k/10); od; if ok=1 then count:=count+1; 
               fi; od; print(n/2-1-count); end: P(1000);
%Y A117644 Sequence in context: A120075 A123650 A122910 this_sequence A055602 A073565 
               A039657
%Y A117644 Adjacent sequences: A117641 A117642 A117643 this_sequence A117645 A117646 
               A117647
%K A117644 nonn
%O A117644 0,1
%A A117644 Paolo P. Lava & Giorgio Balzarotti (ppl(AT)spl.at), Apr 10 2006