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 A217956 Total number of solutions to the equation x^2+k*y^2 = n with x > 0, y > 0, k >= 0, or 0 if infinite. (Order matters for the equation x^2+y^2 = n). 5
 0, 1, 1, 0, 3, 2, 2, 3, 0, 4, 3, 4, 6, 3, 3, 0, 7, 5, 5, 7, 6, 5, 4, 6, 0, 6, 6, 8, 9, 5, 6, 8, 9, 8, 5, 0, 11, 6, 6, 11, 12, 6, 8, 9, 12, 7, 6, 10, 0, 9, 8, 15, 12, 10, 8, 10, 13, 10, 8, 10, 15, 7, 9, 0, 16, 9, 10, 15, 12, 10, 8, 15, 18, 10, 9, 16, 12, 8, 11, 15, 0, 12, 9, 16, 19, 10, 9, 16, 18, 13, 12, 13, 14, 11, 9, 15, 21, 10, 14, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 COMMENTS If the equation x^2+y^2 = n has two solutions (x, y), (y, x) then they will be counted differently. No solutions can exist for the values of k >= n. a(n) is the same as A216674(n) when n is not the sum of two positive squares. But when n is the sum of two positive squares, the ordered pairs for the equation x^2+y^2 = n count. For example, 10 = 3^2 + 1^2. 10 = 1^2 + 3^2. 10 = 2^2 + 6*1^2. 10 = 1^2 + 9*1^2. So a(10) = 4. On the other hand, for the sequence A216674, the ordered pair 3^2+1^2 and 1^2+3^2 will be counted as the same, and so A216674(10) = 3. LINKS PROG (PARI) for(n=1, 100, sol=0; for(k=0, n, for(x=1, n, if((issquare(n-k*x*x)&&n-k*x*x>0), sol++))); if(issquare(n), print1(0", "), print1(sol", "))) /* V. Raman, Oct 16 2012 */ CROSSREFS Cf. A216503, A216504, A216505. Cf. A216674 (a variant of this sequence, when the order does not matter for the equation x^2+y^2 = n, i.e. if the equation x^2+y^2 = n has got two solutions (x, y), (y, x) then they will be counted as the same). Cf. A216672, A216673, A216674, A217834, A217840. Sequence in context: A073756 A328829 A006379 * A105198 A133882 A092106 Adjacent sequences:  A217953 A217954 A217955 * A217957 A217958 A217959 KEYWORD nonn AUTHOR V. Raman, Oct 16 2012 STATUS approved

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Last modified July 27 17:57 EDT 2021. Contains 346308 sequences. (Running on oeis4.)