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A092186
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a(n) = 2(m!)^2 for n = 2m and m!(m+1)! for n = 2m+1.
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6
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2, 1, 2, 2, 8, 12, 72, 144, 1152, 2880, 28800, 86400, 1036800, 3628800, 50803200, 203212800, 3251404800, 14631321600, 263363788800, 1316818944000, 26336378880000, 144850083840000, 3186701844480000, 19120211066880000, 458885065605120000, 2982752926433280000
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OFFSET
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0,1
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COMMENTS
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Singmaster's problem: "A salesman's office is located on a straight road. His n customers are all located along this road to the east of the office, with the office of customer k at distance k from the salesman's office. The salesman must make a driving trip whereby he leaves the office, visits each customer exactly once, then returns to the office.
"Because he makes a profit on his mileage allowance, the salesman wants to drive as far as possible during his trip. What is the maximum possible distance he can travel on such a trip and how many different such trips are there?
"Assume that if the travel plans call for the salesman to visit customer j immediately after he visits customer i, then he drives directly from i to j."
The solution to the first question is twice A002620(n-1); the solution to the second question is a(n).
Number of permutation of [n] with no pair of consecutive elements of the same parity. - Vladeta Jovovic, Nov 26 2007
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REFERENCES
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David Singmaster, Problem 1654, Mathematics Magazine 75 (October 2002). Solution in Mathematics Magazine 76 (October 2003).
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LINKS
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Table of n, a(n) for n=0..25.
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CROSSREFS
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Sequence in context: A145859 A145863 A110775 * A138262 A127510 A158810
Adjacent sequences: A092183 A092184 A092185 * A092187 A092188 A092189
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KEYWORD
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nonn,changed
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AUTHOR
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N. J. A. Sloane, based on correspondence from Hugo Pfoertner and Rob Pratt, Apr 02 2004
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STATUS
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approved
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