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A302985 Number of ordered pairs (x, y) of nonnegative integers such that n - 2^x - 3*2^y has the form u^2 + 2*v^2 with u and v integers.

%I A302985 #7 Apr 19 2018 05:54:10
%S A302985 0,0,0,1,2,2,4,5,4,5,6,4,7,7,7,10,7,6,8,8,6,11,10,8,10,11,8,11,12,11,
%T A302985 12,14,8,10,9,11,11,14,11,12,14,8,12,15,10,14,13,12,11,14,12,17,13,13,
%U A302985 15,15,16,17,13,15
%N A302985 Number of ordered pairs (x, y) of nonnegative integers such that n - 2^x - 3*2^y has the form u^2 + 2*v^2 with u and v integers.
%C A302985 Conjecture: a(n) > 0 for all n > 3.
%C A302985 This is equivalent to the author's conjecture in A302983. We have verified a(n) > 0 for all n = 4...6*10^9.
%C A302985 See also A302982 and A302984 for similar conjectures.
%H A302985 Zhi-Wei Sun, <a href="/A302985/b302985.txt">Table of n, a(n) for n = 1..10000</a>
%H A302985 Zhi-Wei Sun, <a href="http://dx.doi.org/10.1016/j.jnt.2016.11.008">Refining Lagrange's four-square theorem</a>, J. Number Theory 175(2017), 167-190.
%H A302985 Zhi-Wei Sun, <a href="http://maths.nju.edu.cn/~zwsun/179b.pdf">New conjectures on representations of integers (I)</a>, Nanjing Univ. J. Math. Biquarterly 34(2017), no. 2, 97-120.
%H A302985 Zhi-Wei Sun, <a href="http://arxiv.org/abs/1701.05868">Restricted sums of four squares</a>, arXiv:1701.05868 [math.NT], 2017-2018.
%e A302985 a(4) = 1 with 4 - 2^0 - 3*2^0 = 0^2 + 2*0^2.
%e A302985 a(5) = 2 with 5 - 2^0 - 3*2^0 = 1^2 + 2*0^2 and 5 - 2^1 - 3*2^0 = 0^2 + 2*0^2.
%e A302985 a(6) = 2 with 6 - 2^0 - 3*2^0 = 0^2 + 2*1^2 and 6 - 2^1 - 3*2^0 = 1^2 + 2*0^2.
%t A302985   f[n_]:=f[n]=FactorInteger[n];
%t A302985 g[n_]:=g[n]=Sum[Boole[MemberQ[{5,7},Mod[Part[Part[f[n],i],1],8]]&&Mod[Part[Part[f[n],i],2],2]==1],{i,1,Length[f[n]]}]==0;
%t A302985 QQ[n_]:=QQ[n]=(n==0)||(n>0&&g[n]);
%t A302985 tab={};Do[r=0;Do[If[QQ[n-3*2^k-2^j],r=r+1],{k,0,Log[2,n/3]},{j,0,If[3*2^k==n,-1,Log[2,n-3*2^k]]}];tab=Append[tab,r],{n,1,60}];Print[tab]
%Y A302985 Cf. A000079, A000290, A002479, A271518, A281976, A299924, A299537, A299794, A300219, A300362, A300396, A300441, A301376, A301391, A301471, A301472, A302920, A302981, A302982, A302983, A302984.
%K A302985 nonn
%O A302985 1,5
%A A302985 _Zhi-Wei Sun_, Apr 16 2018