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 A178444 Markov numbers that are prime. 6

%I

%S 2,5,13,29,89,233,433,1597,2897,5741,7561,28657,33461,43261,96557,

%T 426389,514229,1686049,2922509,3276509,94418953,321534781,433494437,

%U 780291637,1405695061,2971215073,19577194573,25209506681,44208781349,44560482149,128367472469

%N Markov numbers that are prime.

%C Triples of prime Markov numbers appear to be very rare. For Markov numbers less than 10^1000, only five are known: (2, 5, 29), (5, 29, 433), (5, 2897, 43261), (2, 5741, 33461), and (89, 6017226864647074440629, 1606577036114427599277221). Note that the smallest members of these triples are prime Fibonacci numbers 2, 5, and 89. [_T. D. Noe_, Jan 28 2011]

%C All terms after the first are of the form 4k+1. [_Paul Muljadi_, Jan 31 2011]

%C Bourgain, Gamburd, and Sarnak have announced a proof that almost all Markoff numbers are composite--see A256395. Equivalently, the present sequence has density zero among all Markoff numbers. (It is conjectured that the sequence is infinite.) - _Jonathan Sondow_, Apr 30 2015

%H T. D. Noe, <a href="/A178444/b178444.txt">Table of n, a(n) for n = 1..300</a>

%H J. Bourgain, A. Gamburd, and P. Sarnak, <a href="http://arxiv.org/abs/1505.06411">Markoff triples and strong approximation</a>, arXiv:1505.06411 [math.NT], 2015.

%t m = {1}; Do[x = m[[i]]; y = m[[j]]; a = (3*x*y + Sqrt[ -4*x^2 - 4*y^2 + 9*x^2*y^2])/2; b = (3*x*y + Sqrt[ -4*x^2 - 4*y^2 + 9*x^2*y^2])/2; If[ IntegerQ[a], m = Union[ Join[m, {a}]]]; If[ IntegerQ[b], m = Union[ Join[m, {b}]]], {n, 8}, {i, Length[m]}, {j, i}]; Take[m, 40] (* Robert G. Wilson v, Oct 05 2005, taken from A002559 *); Select[m, PrimeQ]

%Y Cf. A002559, A256395.

%K nonn

%O 1,1

%A _Paul Muljadi_, Jan 01 2011

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Last modified May 26 18:08 EDT 2020. Contains 334630 sequences. (Running on oeis4.)