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 A295819 Number of nonnegative solutions to (x,y) = 1 and x^2 + y^2 = n. 4
 0, 2, 1, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 0, 0, 0, 0, 2, 0, 0, 2, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 2, 2, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 4, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Seiichi Manyama, Table of n, a(n) for n = 0..1000 FORMULA a(n) = A000089(n) for n >= 2. a(A006278(n)) = 2^n for n >= 1. EXAMPLE a(1) = 2; (1,0) = 1 and 1^2 + 0^2 =  1. (0,1) = 1 and 0^2 + 1^2 =  1. a(2) = 1; (1,1) = 1 and 1^2 + 1^2 =  2. ->  1^2 +  1^2 == 1^2 + 1 == 0 mod  2. a(5) = 2; (2,1) = 1 and 2^2 + 1^2 =  5. ->  2^2 +  1^2 == 2^2 + 1 == 0 mod  5. (1,2) = 1 and 1^2 + 2^2 =  5. ->  3^2 +  6^2 == 3^2 + 1 == 0 mod  5. a(10) = 2; (3,1) = 1 and 3^2 + 1^2 = 10. ->  3^2 +  1^2 == 3^2 + 1 == 0 mod 10. (1,3) = 1 and 1^2 + 3^2 = 10. ->  7^2 + 21^2 == 7^2 + 1 == 0 mod 10. a(13) = 2; (3,2) = 1 and 3^2 + 2^2 = 13. -> 21^2 + 14^2 == 8^2 + 1 == 0 mod 13. (2,3) = 1 and 2^2 + 3^2 = 13. -> 18^2 + 27^2 == 5^2 + 1 == 0 mod 13. MATHEMATICA a[n_] := Sum[j = Sqrt[n - i^2] // Floor; Boole[GCD[i, j] == 1 && i^2 + j^2 == n], {i, 0, Sqrt[n]}]; Table[a[n], {n, 0, 100}] (* Jean-François Alcover, Jul 05 2018, after Andrew Howroyd *) PROG (PARI) a(n) = {sum(i=0, sqrtint(n), my(j=sqrtint(n-i^2)); gcd(i, j)==1 && i^2+j^2==n)} \\ Andrew Howroyd, Dec 12 2017 CROSSREFS Cf. A006278. Similar sequences: A000010, A000925, A295820, A295848, A295976. A000089 is essentially the same sequence. Sequence in context: A110855 A054673 A155103 * A048105 A335021 A176202 Adjacent sequences:  A295816 A295817 A295818 * A295820 A295821 A295822 KEYWORD nonn AUTHOR Seiichi Manyama, Nov 28 2017 STATUS approved

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Last modified May 25 06:43 EDT 2022. Contains 354049 sequences. (Running on oeis4.)