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Search: id:A139558
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| A139558 |
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a(1)=4. For n>=2, a(n) = smallest integer > a(n-1) that is not coprime to (n+1) but is coprime to n. |
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2
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| 4, 9, 10, 15, 16, 35, 36, 39, 40, 77, 78, 91, 92, 93, 94, 119, 120, 133, 134, 141, 142, 161, 162, 175, 176, 177, 178, 261, 262, 341, 342, 345, 346, 355, 356, 407, 408, 411, 412, 451, 452, 473, 474, 475, 476, 517, 518, 539, 540, 543, 548, 583, 584, 595, 596, 597
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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a(10^k): 4, 77, 1717, 46871, 1027767, 34696937, 1068983293, ..., and a(2^k): 4, 9, 15, 39, 119, 345, 685, 2415, 5911, 18855, 47995, 124455, 290615, 794529, 2571825, 6910425, 18153749, 50986623, 147584275, 431488203, 1146090309, ..., . - Robert G. Wilson v.
Least term k such that there are just n consecutive terms: 4, 9, 91, 199068, 16621, 14052655, 17301, 6156769, 66781, 330484338, 376051, ???, 273222587, ???, 83335435, ..., . - Robert G. Wilson v.
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MAPLE
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A139558 := proc(n) option remember ; local a, i; if n = 1 then RETURN(4) ; fi ; for a from A139558(n-1)+1 do if gcd(a, n) = 1 and gcd(a, n+1) <> 1 then RETURN(a) ; fi ; od: a ; end: seq(A139558(n), n=1..100) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 20 2008
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MATHEMATICA
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f[1] = 4; f[n_] := f[n] = Block[{k = f[n - 1] + 1}, While[ GCD[n + 1, k] == 1 || GCD[n, k] > 1, k++ ]; k]; Array[f, 56] (* Robert G. Wilson v *)
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CROSSREFS
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Cf. A139557.
Adjacent sequences: A139555 A139556 A139557 this_sequence A139559 A139560 A139561
Sequence in context: A054294 A064973 A133764 this_sequence A119961 A110602 A122635
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Apr 27 2008
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl) and Robert G. Wilson v, (rgwv(AT)rgwv.com), May 20 2008
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