%I A130110
%S A130110 1,2,3,10,4,5,6,21,7,8,9,12,11,13,14,26,15,16,17,33,18,19,20,24,22,23,
%T A130110 25,30,27,28,29,37,31,32,34,47,35,36,38,60,39,40,41,49,42,43,44,67,45,
%U A130110 46,48,57,50,51,52,72,53,54,55,63,56,58,59,83,61,62,64,69,65,66,68,90
%N A130110 Rearrangement of natural numbers such that each four terms sum up to 
               a perfect square.
%e A130110 1+2+3+10=16, 4+5+6+21=36, 7+8+9+12=36, 11+13+14+26=64.
%t A130110 s={};ra=Range[2000]; Do[su=ra[[1]]+ra[[2]]+ra[[3]]; c=4;While[ !IntegerQ[Sqrt[su+ra[[c]]]],
               c++ ];rac=ra[[c]]; s=Join[s,{ra[[1]],ra[[2]],ra[[3]],rac}]; ra=Complement[ra,
               {ra[[1]],ra[[2]],ra[[3]],rac}],{50}];s
%Y A130110 Cf. A130108, A130109, A130111.
%Y A130110 Sequence in context: A054544 A132537 A153702 this_sequence A031275 A119023 
               A048985
%Y A130110 Adjacent sequences: A130107 A130108 A130109 this_sequence A130111 A130112 
               A130113
%K A130110 nonn
%O A130110 1,2
%A A130110 Zak Seidov (zakseidov(AT)yahoo.com), May 08 2007