cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A274050 Numbers that cannot be expressed as the sum of two nonzero squares and at most one power of two.

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%I A274050 #13 Sep 04 2017 09:01:38
%S A274050 1,23,71,79,95,135,142,143,167,190,191,211,215,239,255,284,286,287,
%T A274050 303,311,323,331,343,359,380,382,383,415,419,430,431,439,455,471,475,
%U A274050 499,503,519,527,568,572,574,575,583,591,599,622,623,646,647,671,683,695
%N A274050 Numbers that cannot be expressed as the sum of two nonzero squares and at most one power of two.
%C A274050 The number 1 is considered a power of two.
%H A274050 Chai Wah Wu, <a href="/A274050/b274050.txt">Table of n, a(n) for n = 1..10000</a>
%H A274050 Dave Platt, Tim Trudgian, <a href="https://arxiv.org/abs/1610.01672">On the sum of two squares and at most two powers of 2</a>, arXiv:1610.01672 [math.NT], 2016.
%t A274050 nR[n_] := (SquaresR[2, n] + Plus @@ Pick[{-4, 4}, IntegerQ /@ Sqrt[{n, n/2}]])/8; bad[n_] := nR[n] == 0 && Block[{k = 1}, While[k < n && nR[n - k] == 0, k *= 2]; k >= n]; Select[Range@ 1000, bad]
%Y A274050 Cf. A000404, A273812.
%K A274050 nonn
%O A274050 1,2
%A A274050 _Giovanni Resta_, Jun 08 2016