%I A127689
%S A127689 3,4,12,84,132,12324,15960,26280,27300,66660,115188
%N A127689 a(1)=3; for n>1, a(n) is least number such that a(1)^2+...+a(n)^2 is 
               a square.
%e A127689 a(2)=4 because 3^2+4^2=5^2, a(3)=12 because 3^2+4^2+12^2=13^2 etc.
%t A127689 a = {3}; For[k = 1 + a[[Length[a]]], Length[a] < 11, While[ ! IntegerQ[Sqrt[(k)^2 
               + Sum[(a[[t]])^2, {t, 1, Length[a]}]]], k++ ]; AppendTo[a, k]]; a
%Y A127689 Cf. A018930, A127690, A127691.
%Y A127689 Sequence in context: A122903 A059792 A018930 this_sequence A127690 A092417 
               A071543
%Y A127689 Adjacent sequences: A127686 A127687 A127688 this_sequence A127690 A127691 
               A127692
%K A127689 nonn
%O A127689 1,1
%A A127689 Artur Jasinski (grafix(AT)csl.pl), Jan 23 2007