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%I #6 Nov 21 2013 12:49:03
%S 0,2,6,3,2,3,6,11,9,9,2,6,12,11,3,6,11,9,9,11,6,12,11,12,6,11,9,18,11,
%T 15,12,20,12,6,11,9,9,11,15,12,11,12,15,20,18,9,11,15,12,11,12,15,20,
%U 18,18,11,15,12,11,12,15,20,18,9,11,15,12,20,21,15,20,9,18,11,15,12,20,12
%N Sum of the digits of n*(n+1).
%F a(n)=Sum_digits[n*(n+1)], with n>=0
%p P:=proc(n) local i,k,w; for i from 0 by 1 to n do w:=0;k:=i*(i+1); while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; print(w); od; end: P(100);
%t Table[Total[IntegerDigits[n(n+1)]],{n,0,80}] (* _Harvey P. Dale_, May 14 2011 *)
%K easy,nonn,base
%O 0,2
%A _Paolo P. Lava_ and _Giorgio Balzarotti_, May 03 2007
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