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Search: id:A117365
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| A117365 |
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a(n) = largest prime less than the smallest prime dividing n (or 1 if there is no such prime). |
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+0
5
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| 1, 1, 2, 1, 3, 1, 5, 1, 2, 1, 7, 1, 11, 1, 2, 1, 13, 1, 17, 1, 2, 1, 19, 1, 3, 1, 2, 1, 23, 1, 29, 1, 2, 1, 3, 1, 31, 1, 2, 1, 37, 1, 41, 1, 2, 1, 43, 1, 5, 1, 2, 1, 47, 1, 3, 1, 2, 1, 53, 1, 59, 1, 2, 1, 3, 1, 61, 1, 2, 1, 67, 1, 71, 1, 2, 1, 5, 1, 73, 1, 2, 1, 79, 1, 3, 1, 2, 1, 83, 1, 5, 1, 2, 1, 3, 1
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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a(n) = 1 if and only if n is even or if n = 1.
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EXAMPLE
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5 is the smallest prime dividing 35. So a(35) is the largest prime < 5, which is 3.
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MATHEMATICA
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a[n_] := If[EvenQ[n], 1, Prime[PrimePi[FactorInteger[n][[1]][[1]]] - 1]]; Table[a[n], {n, 2, 80}] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Mar 14 2006
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CROSSREFS
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Cf. A117364, A117366, A117367, A117368.
Sequence in context: A110977 A069230 A101387 this_sequence A116212 A079068 A133021
Adjacent sequences: A117362 A117363 A117364 this_sequence A117366 A117367 A117368
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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), Mar 10 2006
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EXTENSIONS
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More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Mar 14 2006
More terms from Frank Adams-Watters (FrankTAW(AT)Netscape.net), Aug 29 2006
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