%I
%S 75,300,507,675,867,1200,1875,2028,2523,2700,3468,3675,4107,4563,4800,
%T 5043,6075,7500,7803,8112,8427,9075,10092,10800,11163,12675,13872,
%U 14700,15987,16428,16875,18252,19200,20172,21675,22707,23763,24300,24843,27075,28227,30000,30603
%N Numbers that are the sum of three squares in arithmetic progression.
%H Chai Wah Wu, <a href="/A292313/b292313.txt">Table of n, a(n) for n = 1..10000</a>
%F Sequence is 3*(distinct elements in A198385).
%F Numbers of the form 3*m^2 where 2*m^2 is in A004431.  _Chai Wah Wu_, Oct 05 2017
%e 75 = 1^2 + 5^2 + 7^2 = 1 + 25 + 49, with 25  1 = 49  25 = 24.
%e 675 = 3^2 + 15^2 + 21^2 = 9 + 225 + 441, with 225  9 = 441  225 = 216.
%o (PARI) t=4; k=3; while(t<=13000, i=k; e=0; v=t+i; while(i>1&&e==0, if(issquare(v), m=3*t; e=1; print1(m,", ")); i+=2; v+=i); k+=2; t+=k)
%Y Subsequence of A033428.
%Y Cf. A000290, A000378, A004431, A134422, A292309, A292310, A292314, A292316.
%K nonn
%O 1,1
%A _Antonio RoldÃ¡n_, Sep 14 2017
