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A151799
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Version 2 of the "previous prime" function: largest prime < n.
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123
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2, 3, 3, 5, 5, 7, 7, 7, 7, 11, 11, 13, 13, 13, 13, 17, 17, 19, 19, 19, 19, 23, 23, 23, 23, 23, 23, 29, 29, 31, 31, 31, 31, 31, 31, 37, 37, 37, 37, 41, 41, 43, 43, 43, 43, 47, 47, 47, 47, 47, 47, 53, 53, 53, 53, 53, 53, 59, 59, 61, 61, 61, 61, 61, 61, 67, 67, 67, 67, 71, 71, 73, 73, 73, 73
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OFFSET
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3,1
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COMMENTS
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Version 1 of the "previous prime" function is "largest prime <= n". This produces A007917, the same sequence of numerical values, except the offset (or indexing) starts at 2 instead of 3.
Maple's "prevprime" function uses version 2.
See A007917 for references and further information.
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LINKS
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FORMULA
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a(n) = n + 1 - Sum_{k=1..n}( floor(k!^(n-1)/(n-1)!)-floor((k!^(n-1)-1)/(n-1)!) ). - Anthony Browne, May 17 2016
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MAPLE
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MATHEMATICA
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PROG
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(Maxima) makelist(prev_prime(n), n, 3, 79); /* Bruno Berselli, May 20 2011 */
(Haskell)
(Python)
from sympy import prevprime
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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STATUS
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approved
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