A108720 - OEIS

%I #5 Nov 21 2013 12:48:42

%S 1,1,2,4,12,24,42,78,168,393,618,843,1068,1293,1518,1743,1968,2328,

%T 2688,3048,3408,3633,3858,4218,4578,4938,5514,5874,6234,6594,6954,

%U 7530,7890,8250,8610,8835,9195,9771,10347,10707,10932,11157,11382,11607,11832

%N a(n)=a(n-1)+sum of digits(a(n-1))*sum of digits(a(n-2)).

%e a(7)=42,sum of digits(42)=6,a(8)=78,sum of digits(78)=15,

%e a(9)=78+6*15=168

%p a[1]:=1:a[2]:=1:for n from 3 to 100 do d:=a[n-1]:s:=0:while d>0 do c:=d mod 10:s:=s+c:d:=(d-c)/10 od:e:=a[n-2]:t:=0:while e>0 do c:=e mod 10:t:=t+c:e:=(e-c)/10 od:a[n]:=a[n-1]+s*t od: seq(a[n],n=1..100);

%t Transpose[NestList[{Last[#],Last[#]+Total[IntegerDigits[Last[#]]] Total[ IntegerDigits[ First[#]]]}&,{1,1},50]][[1]] (* _Harvey P. Dale_, Dec 09 2011 *)

%K easy,base,nonn

%O 1,3

%A _Miklos Kristof_, Jun 21 2005