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Search: id:A102786
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| A102786 |
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Integer part of n#/((p-3)# 3#), where p=preceding prime to n. |
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+0
1
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| 0, 2, 5, 1, 23, 2, 53, 3, 4, 149, 6, 6, 293, 7, 8, 9, 599, 11, 11, 863, 13, 13, 14, 16, 16, 1733, 17, 1943, 18, 21, 21, 22, 3173, 24, 3749, 26, 27, 27, 28, 29, 5399, 31, 6143, 32, 6533, 35, 37, 37, 8663, 38, 39, 9599, 41, 42, 43, 44, 12149, 46, 46, 13253, 48
(list; graph; listen)
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OFFSET
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2,2
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COMMENT
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0# = 1# = 2 by convention.
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FORMULA
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n# = product of primes <= n. 0#=1#=2. n#/((p-r)# r#) is analogous to the number of combinations of n things taken r at a time: C(n, r) = n!/((n-r)! r!) where factorial ! is replaced by primorial # and n is replaced with the preceding prime to n.
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PROGRAM
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(PARI) c(n, r) = { local(p); forprime(p=r, n, print1(floor(primorial(p)/primorial(p-r)/primorial(r)+.0)", ") ) } primorial(n) = \ The product primes <= n using the pari primelimit. { local(p1, x); if(n==0||n==1, return(2)); p1=1; forprime(x=2, n, p1*=x); return(p1) }
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CROSSREFS
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Sequence in context: A162975 A120294 A047921 this_sequence A159985 A146103 A064334
Adjacent sequences: A102783 A102784 A102785 this_sequence A102787 A102788 A102789
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Feb 25 2005
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