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 A263715 Nonnegative integers that are the sum or difference of two squares. 5
 0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 34, 35, 36, 37, 39, 40, 41, 43, 44, 45, 47, 48, 49, 50, 51, 52, 53, 55, 56, 57, 58, 59, 60, 61, 63, 64, 65, 67, 68, 69, 71, 72, 73, 74, 75, 76, 77, 79, 80 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Contains all integers that are not equal to 2 (mod 4) (they are of the form y^2 - x^2) and those of the form 4k+2 = 2*(2k+1) with the odd number 2k+1 equal to the sum of two squares (A057653). LINKS Jean-Christophe Hervé, Table of n, a(n) for n = 1..10000 FORMULA Union of A001481 (sums of two squares) and A042965 (differences of two squares). Union of A042965 and 2*A057653 = A097269, with intersection of A042965 and A097269 = {}. Union of A020668 (x^2+y^2 and a^2-b^2), A097269 (x^2+y^2, not a^2-b^2) and A263737 (not x^2+y^2, a^2-b^2). EXAMPLE 2 = 1^2 + 1^2, 3 = 2^2 - 1^2, 4 = 2^2 + 0^2, 5 = 2^2 + 1^2 = 3^2 - 2^2. MATHEMATICA r[n_] := Reduce[n == x^2 + y^2, {x, y}, Integers] || Reduce[0 <= y <= x && n == x^2 - y^2, {x, y}, Integers]; Reap[Do[If[r[n] =!= False, Sow[n]], {n, 0, 80}]][[2, 1]] (* Jean-François Alcover, Oct 25 2015 *) CROSSREFS Cf. A001481, A057653, A097269, A042965, A020668, A263737. Cf. A062316 (complement), A079298. Sequence in context: A088451 A047595 A079298 * A023055 A230872 A247832 Adjacent sequences:  A263712 A263713 A263714 * A263716 A263717 A263718 KEYWORD nonn AUTHOR Jean-Christophe Hervé, Oct 24 2015 STATUS approved

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Last modified October 15 23:54 EDT 2019. Contains 328038 sequences. (Running on oeis4.)