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A139172
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Natural numbers of the form (n!-2)/2.
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10
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0, 2, 11, 59, 359, 2519, 20159, 181439, 1814399, 19958399, 239500799, 3113510399, 43589145599, 653837183999, 10461394943999, 177843714047999, 3201186852863999, 60822550204415999, 1216451004088319999
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OFFSET
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2,2
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COMMENTS
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Natural numbers of the form (n!-m)/m:
a(n) = Number of numbers removed in first step of Eratosthenes's sieve for n!
Generally, for n >= m, the formula a(n) = n*(a(n-1) + 1) - 1 applies to all natural numbers of the form (n!-m)/m, m >= 2. - Bob Selcoe, Mar 28 2015
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LINKS
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FORMULA
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a(n) = Sum_{k=1..floor(n/2)} s(n,n-2*k), where s(n,k) are Stirling numbers of the first kind, A048994. - Mircea Merca, Apr 07 2012
a(n) = n*(a(n-1) + 1) - 1. - Bob Selcoe, Mar 28 2015
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MATHEMATICA
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Table[(n! - 2)/2, {n, 2, 20}]
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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