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A109920
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a(1) = 1, then LCM of consecutive composite numbers sandwiched between primes.
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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
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OFFSET
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1,2
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LINKS
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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, May 02 2007
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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