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Search: id:A020639
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| A020639 |
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Lpf(n): least prime dividing n (a(1)=1). |
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+0
213
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| 1, 2, 3, 2, 5, 2, 7, 2, 3, 2, 11, 2, 13, 2, 3, 2, 17, 2, 19, 2, 3, 2, 23, 2, 5, 2, 3, 2, 29, 2, 31, 2, 3, 2, 5, 2, 37, 2, 3, 2, 41, 2, 43, 2, 3, 2, 47, 2, 7, 2, 3, 2, 53, 2, 5, 2, 3, 2, 59, 2, 61, 2, 3, 2, 5, 2, 67, 2, 3, 2, 71, 2, 73, 2, 3, 2, 7, 2, 79, 2, 3, 2, 83, 2, 5, 2, 3, 2, 89, 2, 7, 2, 3, 2, 5, 2, 97
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(1) = 1, a(2) = (2*1)/1 = 2; a(n+1) = a(n)*(the smallest prime divisor of (n+1) divided by the largest prime divisor of a(n)). - Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 28 2004
a(n) = the maximum number of integers such that all pairwise differences are coprime to n. - Max Alekseyev (maxal(AT)cs.ucsd.edu), Mar 17 2006
Also, except for the first term, the smallest prime dividing n. - Cino Hilliard (pseudo.t(AT)comcast.net), Dec 08 2006
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REFERENCES
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D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, Section IV.1.
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LINKS
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T. D. Noe, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
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FORMULA
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A014673(n) = a(A032742(n)); A117357(n) = a(A054576(n)). - Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), Mar 10 2006
A028233(n) = a(n)^A067029(n). - Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), May 13 2006
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PROGRAM
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(PARI) g(n) = for(x=2, n, a=Vec(factor(x)); print1(a[1][1]", ")) - Cino Hilliard (pseudo.t(AT)comcast.net), Dec 08 2006
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CROSSREFS
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Cf. A090368 (bisection).
Cf. A009190, A006530, A034684, A028233, A034699, A053585. See also A046669, A032742.
Cf. A068319, A088377.
Sequence in context: A086286 A135679 A092028 this_sequence A092067 A079879 A071889
Adjacent sequences: A020636 A020637 A020638 this_sequence A020640 A020641 A020642
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KEYWORD
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nonn,easy,nice
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AUTHOR
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David W. Wilson (davidwwilson(AT)comcast.net)
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