

A178444


Markov numbers that are prime.


6



2, 5, 13, 29, 89, 233, 433, 1597, 2897, 5741, 7561, 28657, 33461, 43261, 96557, 426389, 514229, 1686049, 2922509, 3276509, 94418953, 321534781, 433494437, 780291637, 1405695061, 2971215073, 19577194573, 25209506681, 44208781349, 44560482149, 128367472469
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OFFSET

1,1


COMMENTS

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]
All terms after the first are of the form 4k+1. [Paul Muljadi, Jan 31 2011]
Bourgain, Gamburd, and Sarnak have announced a proof that almost all Markoff numbers are compositesee 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


LINKS

T. D. Noe, Table of n, a(n) for n = 1..300
J. Bourgain, A. Gamburd, and P. Sarnak, Markoff triples and strong approximation, arXiv:1505.06411 [math.NT], 2015.


MATHEMATICA

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]


CROSSREFS

Cf. A002559, A256395.
Sequence in context: A045703 A289843 A242080 * A299145 A122025 A236414
Adjacent sequences: A178441 A178442 A178443 * A178445 A178446 A178447


KEYWORD

nonn


AUTHOR

Paul Muljadi, Jan 01 2011


STATUS

approved



