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 A245585 Numbers that cannot be written as sum of two quarter-squares, cf. A002620. 3

%I

%S 19,23,33,35,47,59,63,71,75,77,95,103,107,118,124,129,131,143,147,155,

%T 161,167,179,187,195,201,203,206,209,215,217,223,236,239,243,247,248,

%U 251,271,275,280,283,285,287,294,299,311,316,323,327,329,332,334,339

%N Numbers that cannot be written as sum of two quarter-squares, cf. A002620.

%C A245575(a(n)) = 0.

%H Reinhard Zumkeller, <a href="/A245585/b245585.txt">Table of n, a(n) for n = 1..10000</a>

%t qsQ[n_] := qsQ[n] = With[{s = Sqrt[n]}, Which[IntegerQ[s], True, n == Floor[s] (Floor[s] + 1), True, True, False]];

%t A245575[n_] := Count[Range[0, n], k_ /; qsQ[k] && qsQ[n - k]];

%t Flatten[Position[Array[A245575, 1000, 0], 0]] - 1 (* _Jean-François Alcover_, May 08 2017 *)

%o a245585 n = a245585_list !! (n-1)

%o a245585_list = filter ((== 0) . a245575) [0..]

%Y Cf. A002620, A245575.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Aug 04 2014

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Last modified June 24 14:24 EDT 2021. Contains 345417 sequences. (Running on oeis4.)