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A117368
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a(n) = largest prime less than the smallest prime dividing (2n-1).
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1
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2, 3, 5, 2, 7, 11, 2, 13, 17, 2, 19, 3, 2, 23, 29, 2, 3, 31, 2, 37, 41, 2, 43, 5, 2, 47, 3, 2, 53, 59, 2, 3, 61, 2, 67, 71, 2, 5, 73, 2, 79, 3, 2, 83, 5, 2, 3, 89, 2, 97, 101, 2, 103, 107, 2, 109, 3, 2, 5, 7, 2, 3, 113, 2, 127, 5, 2, 131, 137, 2, 7, 3, 2, 139, 149, 2, 3, 151, 2, 5, 157, 2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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COMMENTS
| Placing a 1 between each term of this sequence gets sequence A117365.
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EXAMPLE
| a(13)=3 because smallest prime dividing 25 is 5 and largest prime less than 5 is 3.
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MAPLE
| with(numtheory): a:=proc(n): prevprime(factorset(2*n-1)[1]): end: seq(a(n), n=2..90); - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 22 2006
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MATHEMATICA
| prs=Prime[Range[50]];
f[n_]:=NextPrime[First[Select[prs, Divisible[2 n-1, #]&]], -1]
f/@Range[2, 90] [From Harvey P. Dale, Jan. 23, 2011]
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CROSSREFS
| Cf. A117365.
Sequence in context: A176195 A174562 A069227 * A137826 A021429 A124055
Adjacent sequences: A117365 A117366 A117367 * A117369 A117370 A117371
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Mar 10 2006
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EXTENSIONS
| More terms from Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 22 2006
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