A339273 - OEIS

A339273

Sums of two nonzero even squares.

8, 20, 32, 40, 52, 68, 72, 80, 100, 104, 116, 128, 136, 148, 160, 164, 180, 200, 208, 212, 232, 244, 260, 272, 288, 292, 296, 320, 328, 340, 356, 360, 388, 392, 400, 404, 416, 424, 436, 452, 464, 468, 488, 500, 512, 520, 544, 548, 580, 584, 592, 596, 612, 628, 640, 648, 656

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..57.

FORMULA

a(n) = 4*A000404(n).

Characteristic function: sign(Sum_{k=1..floor(n/2)} ((k+1) mod 2) * ((n-k+1) mod 2) * c(k) * c(n-k)), where c is the characteristic function of squares (A010052).

EXAMPLE

20 is in the sequence since it is the sum of two nonzero even squares, 2^2 + 4^2 = 4 + 16 = 20.

MATHEMATICA

Table[If[Sum[Mod[i + 1, 2] Mod[n - i + 1, 2] (Floor[Sqrt[i]] - Floor[Sqrt[i - 1]]) (Floor[Sqrt[n - i]] - Floor[Sqrt[n - i - 1]]), {i, Floor[n/2]}] > 0, n, {}], {n, 700}] // Flatten

CROSSREFS

Cf. A000404, A010052, A057653, A097269.

Sequence in context: A246308 A365145 A194218 * A017617 A246309 A363518

Adjacent sequences: A339270 A339271 A339272 * A339274 A339275 A339276

KEYWORD

nonn,easy

AUTHOR

Wesley Ivan Hurt, Dec 24 2020

STATUS

approved