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Search: id:A160574
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| A160574 |
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Positive numbers y such that y^2 is of the form x^2+(x+313)^2 with integer x. |
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4
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| 233, 313, 493, 905, 1565, 2725, 5197, 9077, 15857, 30277, 52897, 92417, 176465, 308305, 538645, 1028513, 1796933, 3139453, 5994613, 10473293, 18298073, 34939165, 61042825, 106648985, 203640377, 355783657, 621595837, 1186903097
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OFFSET
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1,1
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COMMENT
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(-105, a(1)) and (A129640(n), a(n+1)) are solutions (x, y) to the Diophantine equation x^2+(x+313)^2 = y^2.
lim_{n -> infinity} a(n)/a(n-3) = 3+2*sqrt(2).
lim_{n -> infinity} a(n)/a(n-1) = (363+130*sqrt(2))/313 for n mod 3 = {0, 2}.
lim_{n -> infinity} a(n)/a(n-1) = (119187+47998*sqrt(2))/313^2 for n mod 3 = 1.
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FORMULA
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a(n) = 6*a(n-3)-a(n-6) for n > 6; a(1)=233, a(2)=313, a(3)=493, a(4)=905, a(5)=1565, a(6)=2725.
G.f.: (1-x)*(233+546*x+1039*x^2+546*x^3+233*x^4) / (1-6*x^3+x^6).
a(3*k-1) = 313*A001653(k) for k >= 1.
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EXAMPLE
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(-105, a(1)) = (-105, 233) is a solution: (-105)^2+(-105+313)^2 = 11025+43264 = 54289 = 233^2.
(A129640(1), a(2)) = (0, 313) is a solution: 0^2+(0+313)^2 = 97969 = 313^2.
(A129640(3), a(4)) = (464, 905) is a solution: 464^2+(464+313)^2 = 215296+603729 = 819025 = 905^2.
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PROGRAM
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(PARI) {forstep(n=-108, 10000000, [3, 1], if(issquare(2*n^2+626*n+97969, &k), print1(k, ", ")))}
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CROSSREFS
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Cf. A129640, A001653, A156035 (decimal expansion of 3+2*sqrt(2)), A160575 (decimal expansion of (363+130*sqrt(2))/313), A160576 (decimal expansion of (119187+47998*sqrt(2))/313^2).
Sequence in context: A140033 A142182 A105981 this_sequence A087862 A141280 A097446
Adjacent sequences: A160571 A160572 A160573 this_sequence A160575 A160576 A160577
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KEYWORD
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nonn
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AUTHOR
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Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Jun 08 2009
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