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Search: id:A109919
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| A109919 |
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a(1) = 1, then product 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, 720, 11, 12, 13, 3360, 17, 18, 19, 9240, 23, 11793600, 29, 30, 31, 45239040, 37, 59280, 41, 42, 43, 91080, 47, 311875200, 53, 549853920, 59, 60, 61, 1072431360, 67, 328440, 71, 72, 73, 2533330800, 79, 531360, 83, 4701090240, 89
(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) = a(3) = 1 as empty product is defined to be 1.
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FORMULA
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a(2n) = prime(n) a(2n+1)= product of composite numbers between prime(n) and prime(n+1).
a(2n) = A000040(n). a(2n+1) = A072472(n)/A000040(n+1). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 02 2007
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MAPLE
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A109919 := proc(n) local p; if n mod 2 = 0 then ithprime(n/2) ; elif n = 1 then 1 ; else p := ithprime((n-1)/2) ; mul(i, i=p+1..nextprime(p)-1) ; fi ; end: for n from 1 to 80 do printf("%d, ", A109919(n)) ; od ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), May 02 2007
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CROSSREFS
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Cf. A109920.
Cf. A072472.
Sequence in context: A035043 A058684 A109920 this_sequence A082750 A048212 A077159
Adjacent sequences: A109916 A109917 A109918 this_sequence A109920 A109921 A109922
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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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