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Search: id:A109920
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| A109920 |
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a(1) = 1, then LCM of consecutive composite numbers sandwitched between primes. |
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+0
3
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| 1, 2, 1, 3, 4, 5, 6, 7, 360, 11, 12, 13, 1680, 17, 18, 19, 4620, 23, 491400, 29, 30, 31, 1884960, 37, 29640, 41, 42, 43, 45540, 47, 12994800, 53, 45821160, 59, 60, 61, 89369280, 67, 164220, 71, 72, 73, 211110900, 79, 265680, 83, 195878760, 89
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(2n) = prime(n) a(2n+1)= LCM of composite numbers between prime(n) and prime(n+1). a(1) = a(3) = 1 by choice.
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MAPLE
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A109920 := proc(n) local p; if n mod 2 = 0 then ithprime(n/2) ; elif n = 1 then 1 ; else p := ithprime((n-1)/2) ; lcm(seq(i, i=p+1..nextprime(p)-1)) ; fi ; end: for n from 1 to 80 do printf("%d, ", A109920(n)) ; od ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 02 2007
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CROSSREFS
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Cf. A109919.
Sequence in context: A101204 A035043 A058684 this_sequence A109919 A082750 A048212
Adjacent sequences: A109917 A109918 A109919 this_sequence A109921 A109922 A109923
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KEYWORD
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easy,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jul 16 2005
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 02 2007
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