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 A159809 Positive numbers y such that y^2 is of the form x^2+(x+223)^2 with integer x. 4
 197, 223, 257, 925, 1115, 1345, 5353, 6467, 7813, 31193, 37687, 45533, 181805, 219655, 265385, 1059637, 1280243, 1546777, 6176017, 7461803, 9015277, 35996465, 43490575, 52544885, 209802773, 253481647, 306254033, 1222820173, 1477399307 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS (-28, a(1)) and (A130609(n), a(n+1)) are solutions (x, y) to the Diophantine equation x^2+(x+223)^2 = y^2. Lim_{n -> infinity} a(n)/a(n-3) = 3+2*sqrt(2). Lim_{n -> infinity} a(n)/a(n-1) = (227+30*sqrt(2))/223 for n mod 3 = {0, 2}. Lim_{n -> infinity} a(n)/a(n-1) = (105507+65798*sqrt(2))/223^2 for n mod 3 = 1. For the generic case x^2 + (x+p)^2 = y^2 with p = m^2 - 2 a prime number in A028871, m >= 5, the x values are given by the sequence defined by a(n) = 6*a(n-3) - a(n-6) + 2*p with a(1)=0, a(2) = 2*m + 2, a(3) = 3*m^2 - 10*m + 8, a(4) = 3*p, a(5) = 3*m^2 + 10*m + 8, a(6) = 20*m^2 - 58*m + 42. Y values are given by the sequence defined by b(n) = 6*b(n-3) - b(n-6) with b(1) = p, b(2) = m^2 + 2*m + 2, b(3) = 5*m^2 - 14*m + 10, b(4) = 5*p, b(5) = 5m^2 + 14*m + 10, b(6) = 29*m^2 - 82*m + 58. - Mohamed Bouhamida, Sep 09 2009 LINKS G. C. Greubel, Table of n, a(n) for n = 1..3900 Index entries for linear recurrences with constant coefficients, signature (0,0,6,0,0,-1). FORMULA a(n) = 6*a(n-3) - a(n-6) for n > 6; a(1)=197, a(2)=223, a(3)=257, a(4)=925, a(5)=1115, a(6)=1345. G.f.: (1-x)*(197+420*x+677*x^2+420*x^3+197*x^4) / (1-6*x^3+x^6). a(3*k-1) = 223*A001653(k) for k >= 1. EXAMPLE (-28, a(1)) = (-28, 197) is a solution: (-28)^2 + (-28+223)^2 = 784 + 38025 = 38809 = 197^2. (A130609(1), a(2)) = (0, 223) is a solution: 0^2 + (0+223)^2 = 49729 = 223^2. (A130609(3), a(4)) = (533, 925) is a solution: 533^2 + (533+223)^2 = 284089 + 571536 = 855625 = 925^2. MATHEMATICA LinearRecurrence[{0, 0, 6, 0, 0, -1}, {197, 223, 257, 925, 1115, 1345}, 50] (* G. C. Greubel, May 21 2018 *) PROG (PARI) {forstep(n=-28, 10000000, [1, 3], if(issquare(2*n^2+446*n+49729, &k), print1(k, ", ")))}; (MAGMA) I:=[197, 223, 257, 925, 1115, 1345]; [n le 6 select I[n] else 6*Self(n-3) - Self(n-6): n in [1..30]]; // G. C. Greubel, May 21 2018 CROSSREFS Cf. A130609, A001653, A156035 (decimal expansion of 3+2*sqrt(2)), A130610 (decimal expansion of (227+30*sqrt(2))/223), A130611 (decimal expansion of (105507+65798*sqrt(2))/223^2). Sequence in context: A182572 A152625 A082246 * A345551 A051371 A127339 Adjacent sequences:  A159806 A159807 A159808 * A159810 A159811 A159812 KEYWORD nonn,easy AUTHOR Klaus Brockhaus, Apr 30 2009 STATUS approved

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Last modified June 23 07:38 EDT 2021. Contains 345395 sequences. (Running on oeis4.)