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%I #7 Apr 16 2018 09:45:04
%S 2,7,8,17,18,23,28,32,50,63,68,72,82,92,97,98,103,112,122,128,137,153,
%T 162,175,177,178,200,207,242,252,257,272,288,303,328,337,338,343,367,
%U 368,369,388,392,393,412,417,425,433,448,450,478,487,488,503,512,548,567,575
%N Numbers the square of which can be written as a sum of four nonzero bi-quadratics.
%C Numbers w which can be expressed as w^2 = x^4 +y^4 +z^4 +t^4 with x,y,z,t >0. Values that have more than one representation (w=63, 153, 207, 252,...) are listed only once.
%H A. Alvarado, J.-J. Delorme, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL17/Alvarado/alva3.html">On the diophantine equation x^4+y^4+z^4+t^4=w^2</a>, J. Int. Seq. 17 (2014) # 14.11.5.
%e 2^2 = 1^4 +1^4 +1^4 +1^4. 7^2 = 1^4 +2^4 +2^4 +2^4. 8^2 = 2^4 +2^4 +2^4 +2^4. 17^2 = 1^2 +2^4 +2^4 +4^4. 18^2=3^4 +3^4 +3^4 +3^4. 23^2 = 1^2 +2^4 +4^4 +4^4.
%K nonn
%O 1,1
%A _R. J. Mathar_, Mar 06 2018
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