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A046712 From the Bruck-Ryser theorem: n == 1 or 2 (mod 4) which are not the sum of 2 squares. 3

%I

%S 6,14,21,22,30,33,38,42,46,54,57,62,66,69,70,77,78,86,93,94,102,105,

%T 110,114,118,126,129,133,134,138,141,142,150,154,158,161,165,166,174,

%U 177,182,186,189,190,198,201,206,209,210,213,214,217,222,230,237,238

%N From the Bruck-Ryser theorem: n == 1 or 2 (mod 4) which are not the sum of 2 squares.

%C Intersection of A022544 and A046712. - _Reinhard Zumkeller_, Aug 16 2011

%D M. Hall, Jr., Combinatorial Theory, Wiley, New York, 1986, see Theorem 12.3.2.

%H Reinhard Zumkeller, <a href="/A046712/b046712.txt">Table of n, a(n) for n = 1..10000</a>

%H R. H. Bruck and H. J. Ryser, <a href="http://dx.doi.org/10.4153/CJM-1949-009-2">The nonexistence of certain projective planes</a>, Canad. J. Math., 1 (1949), 88-93.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Bruck-Ryser-ChowlaTheorem.html">Bruck-Ryser-Chowla Theorem</a>

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Bruck-Ryser-Chowla_theorem">Bruck-Ryser-Chowla theorem</a>

%H <a href="/index/Su#ssq">Index entries for sequences related to sums of squares</a>

%t Select[Range[240], (Mod[#, 4] == 1 || Mod[#, 4] == 2) && PowersRepresentations[#, 2, 2] == {} & ] (* _Jean-Fran├žois Alcover_, Aug 30 2011 *)

%t Select[Range[250],MemberQ[{1,2},Mod[#,4]]&&SquaresR[2,#]==0&] (* _Harvey P. Dale_, Apr 01 2015 *)

%o (Haskell)

%o a046712 n = a046712_list !! (n-1)

%o a046712_list = filter ((`elem` [1,2]) . (`mod` 4)) a022544_list

%o -- _Reinhard Zumkeller_, Aug 16 2011

%K nonn,easy,nice

%O 1,1

%A _N. J. A. Sloane_

%E More terms from _James A. Sellers_

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Last modified July 9 16:50 EDT 2020. Contains 335545 sequences. (Running on oeis4.)