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A162489
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Least y such that x^y+y^x is prime, for x = A162488(n).
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4
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2, 2, 2, 2, 5, 15, 2, 33, 7, 3, 21, 8, 34, 9, 80, 56, 67, 9, 32, 65, 45, 133, 98, 36, 51, 157, 76, 214, 200, 87, 91, 111, 122, 342, 20, 142, 364, 289, 9, 184, 98, 423, 365, 20, 56, 441, 329, 8, 234, 234, 157, 291, 91, 379, 98, 464, 518, 325, 32, 654, 87, 634, 34, 21, 443
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Sequences A162488 and A162490 list the corresponding x values and primes.
See there and the main entry A094133 for more information, links and references.
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FORMULA
| a(n)^A162488(n)+A162488(n)^a(n) = A162490(n)
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EXAMPLE
| The least x such that x^y+y^x is prime for some x>y>1 is A162488(1)=3, the smallest such y is a(1)=2, yielding the prime A162490(1) = 9 + 8 = 17.
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MATHEMATICA
| lst = {}; Do[ If[ PrimeQ[x^y + y^x], AppendTo[lst, {x, y}]], {x, 3, 750}, {y, 2, x - 1}]; Transpose[ lst][[2]] [From Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 17 2009]
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PROG
| (PARI) for(i=3, 999, for(j=2, i-1, isprime(i^j+j^i)|next; print1(j", "); break))
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CROSSREFS
| Cf. A094133, A162486 - A162490.
Sequence in context: A195601 A126788 A098789 * A079894 A114005 A103794
Adjacent sequences: A162486 A162487 A162488 * A162490 A162491 A162492
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KEYWORD
| nonn
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AUTHOR
| M. F. Hasler (www.univ-ag.fr/~mhasler), Jul 04 2009
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 17 2009
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