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Nonnegative values x of solutions (x, y) to the Diophantine equation x^2 + (x + 41)^2 = y^2.
+10
12
0, 36, 39, 123, 319, 336, 820, 1960, 2059, 4879, 11523, 12100, 28536, 67260, 70623, 166419, 392119, 411720, 970060, 2285536, 2399779, 5654023, 13321179, 13987036, 32954160, 77641620, 81522519, 192071019, 452528623, 475148160, 1119472036
COMMENTS
Also values x of Pythagorean triples (x, x+41, y).
Corresponding values y of solutions (x, y) are in A157257. lim_{n -> infinity} a(n)/a(n-3) = 3 + 2*sqrt(2).
lim_{n -> infinity} a(n)/a(n-1) = (7 + 2*sqrt(2))/(7 - 2*sqrt(2)) for n mod 3 = {1, 2}.
lim_{n -> infinity} a(n)/a(n-1) = (3 + 2*sqrt(2))*(7 - 2*sqrt(2))^2/(7 + 2*sqrt(2))^2 for n mod 3 = 0.
FORMULA
a(n) = 6*a(n-3) - a(n-6) + 82 for n > 6; a(1)=0, a(2)=36, a(3)=39, a(4)=123, a(5)=319, a(6)=336.
G.f.: x*(36 + 3*x + 84*x^2 - 20*x^3 - x^4 - 20*x^5)/((1-x)*(1 - 6*x^3 + x^6)).
a(3*k + 1) = 41* A001652(k) for k >= 0.
MATHEMATICA
LinearRecurrence[{1, 0, 6, -6, 0, -1, 1}, {0, 36, 39, 123, 319, 336, 820}, 40] (* Harvey P. Dale, Jan 18 2015 *)
PROG
(PARI) forstep(n=0, 1200000000, [3 , 1], if(issquare(2*n^2+82*n+1681), print1(n, ", ")))
(Magma) m:=25; R<x>:=PowerSeriesRing(Integers(), m); [0] cat Coefficients(R!(x*(36+3*x+84*x^2-20*x^3-x^4-20*x^5)/((1-x)*(1-6*x^3+ x^6)))); // G. C. Greubel, May 07 2018
CROSSREFS
Cf. A157257, A001652, A156035 (decimal expansion of 3 + 2*sqrt(2)), A157258 (decimal expansion of 7 + 2*sqrt(2)), A157259 (decimal expansion of 7 - 2*sqrt(2)), A157260 (decimal expansion of (7 + 2*sqrt(2))/(7 - 2*sqrt(2))).
Decimal expansion of 7 - 2*sqrt(2).
+10
9
4, 1, 7, 1, 5, 7, 2, 8, 7, 5, 2, 5, 3, 8, 0, 9, 9, 0, 2, 3, 9, 6, 6, 2, 2, 5, 5, 1, 5, 8, 0, 6, 0, 3, 8, 4, 2, 8, 6, 0, 6, 5, 6, 2, 4, 9, 2, 4, 6, 1, 0, 3, 8, 5, 3, 6, 4, 6, 6, 4, 0, 5, 2, 4, 0, 1, 8, 5, 3, 5, 0, 4, 3, 0, 7, 5, 7, 8, 5, 9, 2, 2, 2, 9, 9, 2, 2, 4, 9, 3, 1, 3, 4, 4, 7, 1, 6, 8, 5, 4, 5, 2, 9, 9, 7
COMMENTS
lim_{n -> infinity} b(n)/b(n-1) = (7+2*sqrt(2))/(7-2*sqrt(2)) for n mod 3 = {1, 2}, b = A129288. lim_{n -> infinity} b(n)/b(n-1) = (7+2*sqrt(2))/(7-2*sqrt(2)) for n mod 3 = {0, 2}, b = A157257.
LINKS
Pierre-Antoine Guihéneuf, Rotations Discrètes, Images des Mathématiques, CNRS, 2018. See 3-2*sqrt(2), the fractional part of this constant, about the loss of information when rotating an image.
FORMULA
Equals 3 + Sum_{k>=0} binomial(2*k,k)/((k+1) * 8^k). - Amiram Eldar, Aug 03 2020
EXAMPLE
7 - 2*sqrt(2) = 4.17157287525380990239...
MATHEMATICA
RealDigits[7-2*Sqrt[2], 10, 120][[1]] (* Harvey P. Dale, May 01 2012 *)
Decimal expansion of 7 + 2*sqrt(2).
+10
8
9, 8, 2, 8, 4, 2, 7, 1, 2, 4, 7, 4, 6, 1, 9, 0, 0, 9, 7, 6, 0, 3, 3, 7, 7, 4, 4, 8, 4, 1, 9, 3, 9, 6, 1, 5, 7, 1, 3, 9, 3, 4, 3, 7, 5, 0, 7, 5, 3, 8, 9, 6, 1, 4, 6, 3, 5, 3, 3, 5, 9, 4, 7, 5, 9, 8, 1, 4, 6, 4, 9, 5, 6, 9, 2, 4, 2, 1, 4, 0, 7, 7, 7, 0, 0, 7, 7, 5, 0, 6, 8, 6, 5, 5, 2, 8, 3, 1, 4, 5, 4, 7, 0, 0, 2
COMMENTS
lim_{n -> infinity} b(n)/b(n-1) = (7+2*sqrt(2))/(7-2*sqrt(2)) for n mod 3 = {1, 2}, b = A129288. lim_{n -> infinity} b(n)/b(n-1) = (7+2*sqrt(2))/(7-2*sqrt(2)) for n mod 3 = {0, 2}, b = A157257.
EXAMPLE
7 + 2*sqrt(2) = 9.82842712474619009760...
MATHEMATICA
RealDigits[7+2Sqrt[2], 10, 120][[1]] (* Harvey P. Dale, Mar 20 2011 *)
Positive numbers y such that y^2 is of the form x^2+(x+41)^2 with integer x.
+10
6
29, 41, 85, 89, 205, 481, 505, 1189, 2801, 2941, 6929, 16325, 17141, 40385, 95149, 99905, 235381, 554569, 582289, 1371901, 3232265, 3393829, 7996025, 18839021, 19780685, 46604249, 109801861, 115290281, 271629469, 639972145, 671961001
COMMENTS
(-20, a(1)) and ( A129288(n), a(n+1)) are solutions (x, y) to the Diophantine equation x^2+(x+41)^2 = y^2. lim_{n -> infinity} a(n)/a(n-3) = 3+2*sqrt(2).
lim_{n -> infinity} a(n)/a(n-1) = (7+2*sqrt(2))/(7-2*sqrt(2)) for n mod 3 = {0, 2}.
lim_{n -> infinity} a(n)/a(n-1) = (3+2*sqrt(2))*(7-2*sqrt(2))^2/(7+2*sqrt(2))^2 for n mod 3 = 1.
FORMULA
a(n) = 6*a(n-3) - a(n-6) for n > 6; a(1)=29, a(2)=41, a(3)=85, a(4)=89, a(5)=205, a(6)=481.
G.f.: (1-x)*(29+70*x+155*x^2+70*x^3+29*x^4)/(1-6*x^3+x^6).
a(3*k-1) = 41* A001653(k) for k >= 1.
EXAMPLE
(-20, a(1)) = (-20, 29) is a solution: (-20)^2+(-20+41)^2 = 400+441 = 841 = 29^2.
( A129288(1), a(2)) = (0, 41) is a solution: 0^2+(0+41)^2 = 1681 = 41^2. ( A129288(3), a(4)) = (39, 89) is a solution: 39^2+(39+41)^2 = 1521+6400 = 7921 = 89^2.
MATHEMATICA
CoefficientList[Series[(1-x)*(29+70*x+155*x^2+70*x^3+29*x^4)/(1-6*x^3+ x^6), {x, 0, 50}], x] (* G. C. Greubel, Feb 04 2018 *)
PROG
(PARI) {forstep(n=-20, 500000000, [3 , 1], if(issquare(n^2+(n+41)^2, &k), print1(k, ", ")))}
(PARI) x='x+O('x^30); Vec((1-x)*(29+70*x+155*x^2+70*x^3+29*x^4)/(1-6*x^3+ x^6)) \\ G. C. Greubel, Feb 04 2018 (Magma) Q:=Rationals(); R<x>:=PowerSeriesRing(Q, 40); Coefficients(R!((1-x)*(29+70*x+155*x^2+70*x^3+29*x^4)/(1-6*x^3+ x^6))) // G. C. Greubel, Feb 04 2018
CROSSREFS
Cf. A129288, A001653, A156035 (decimal expansion of 3+2*sqrt(2)), A157258 (decimal expansion of 7+2*sqrt(2)), A157259 (decimal expansion of 7-2*sqrt(2)), A157260 (decimal expansion of (7+2*sqrt(2))/(7-2*sqrt(2))).
Decimal expansion of (1683 + 58*sqrt(2))/41^2.
+10
2
1, 0, 4, 9, 9, 8, 4, 7, 6, 3, 0, 0, 8, 7, 0, 8, 8, 1, 1, 9, 1, 5, 8, 2, 2, 6, 9, 2, 4, 4, 7, 4, 4, 9, 4, 2, 8, 0, 5, 2, 9, 6, 9, 0, 4, 7, 4, 5, 5, 0, 0, 4, 7, 5, 2, 0, 7, 8, 6, 7, 1, 8, 7, 6, 7, 4, 2, 0, 9, 5, 4, 6, 9, 2, 1, 5, 2, 3, 0, 3, 4, 3, 9, 9, 3, 6, 4, 8, 1, 1, 2, 4, 2, 7, 7, 2, 3, 5, 0, 4, 5, 9, 1, 6, 8
COMMENTS
Limit_{n -> oo} b(n)/b(n-1) = (1683+58*sqrt(2))/41^2 for n mod 3 = 0, b = A129288. Limit_{n -> oo} b(n)/b(n-1) = (1683+58*sqrt(2))/41^2 for n mod 3 = 1, b = A157257.
FORMULA
Equals (58+sqrt(2))/(58-sqrt(2)).
Equals (3+2*sqrt(2))*(7-2*sqrt(2))^2/(7+2*sqrt(2))^2.
EXAMPLE
(1683+58*sqrt(2))/41^2 = 1.04998476300870881191...
MATHEMATICA
RealDigits[(1683+58Sqrt[2])/41^2, 10, 120][[1]] (* Harvey P. Dale, May 05 2014 *)
PROG
(PARI) default(realprecision, 100); (1683+58*sqrt(2))/41^2 \\ G. C. Greubel, Sep 28 2018 (Magma) SetDefaultRealField(RealField(100)); (1683+58*Sqrt(2))/41^2; // G. C. Greubel, Sep 28 2018
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