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A056869
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Prime hypotenuses of Pythagorean triangles with consecutive integer sides.
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3
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5, 29, 5741, 33461, 44560482149, 1746860020068409, 68480406462161287469, 13558774610046711780701, 4125636888562548868221559797461449, 4760981394323203445293052612223893281
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OFFSET
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1,1
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COMMENTS
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Essentially the same sequence as A086383.
If p is a term then it is a unique-period prime in base sqrt(2*p^2 - 1). (End)
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LINKS
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FORMULA
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EXAMPLE
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29 is included because it is prime and it is the hypotenuse of the 20, 21, 29 Pythagorean triangle.
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MAPLE
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f:= gfun:-rectoproc({a(n)=6*a(n-1)-a(n-2), a(1)=1, a(2)=5}, a(n), remember):
select(isprime, [seq(f(n), n=1..1000)]); # Robert Israel, Oct 13 2015
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MATHEMATICA
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Select[Sqrt[#^2+(#+1)^2]&/@With[{p=3+2Sqrt[2]}, NestList[Floor[p #]+3&, 3, 120]], PrimeQ] (* Harvey P. Dale, May 02 2018 *)
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PROG
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(PARI) t(n) = if(n<3, 5^(n-1), 6*t(n-1)-t(n-2));
for(n=1, 50, if(isprime(t(n)), print1(t(n)", "))) \\ Altug Alkan, Oct 13 2015
(GAP) f:=[1, 5];; for n in [3..60] do f[n]:=6*f[n-1]-f[n-2]; od; a:=Filtered(f, IsPrime);; Print(a); # Muniru A Asiru, Jan 03 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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Incorrect link to index entries for linear recurrences with constant coefficients removed by Colin Barker, Oct 13 2015
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STATUS
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approved
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