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Search: id:A102787
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| A102787 |
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Integer part of n#/((p-5)# 5#), where p=preceding prime to n. |
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+0
1
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| 0, 0, 0, 3, 2, 4, 7, 10, 14, 0, 29, 1, 50, 58, 67, 1, 1, 119, 2, 158, 172, 2, 218, 2, 3, 326, 346, 367, 388, 410, 4, 554, 4, 634, 4, 749, 5, 5, 907, 5, 5, 1079, 6, 1228, 1267, 1306, 7, 7, 1687, 1732, 1778, 7, 1919, 8, 8, 8, 8, 2429, 9, 2594, 2650, 9
(list; graph; listen)
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OFFSET
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2,4
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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 prime preceding 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 of 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: A105025 A129594 A158441 this_sequence A014193 A128885 A084695
Adjacent sequences: A102784 A102785 A102786 this_sequence A102788 A102789 A102790
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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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