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 A191798 Number of essentially different ways of arranging numbers 1 through 2*n around a circle so that the sums of each pair of adjacent numbers are neither all prime nor all composite. 0
 0, 2, 58, 2474, 180480, 19895936, 3105348340, 652948189204, 177662757810868, 60772232945639507, 25533219938917963508, 12921764841857675170314, 7754002391777621430686566 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Finding a pattern, recurrence relation or explicit formula for this sequence would allow us to find terms in A191374 using terms from A051252, or vice versa. LINKS Table of n, a(n) for n=1..13. FORMULA For n>1, a(n) = (2*n-1)!/2 - A051252(n) - A191374(n). EXAMPLE a(2) = 2 since the arrangements 1,3,2,4 and 1,3,4,2 both satisfy the condition. CROSSREFS Cf. A051252, A191374. Sequence in context: A285148 A115610 A341082 * A206531 A290306 A113635 Adjacent sequences: A191795 A191796 A191797 * A191799 A191800 A191801 KEYWORD nonn,more AUTHOR Bennett Gardiner, Jun 16 2011 EXTENSIONS a(7) corrected, a(8)-a(13) added by Max Alekseyev, Aug 19 2013 STATUS approved

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Last modified May 28 19:24 EDT 2024. Contains 372919 sequences. (Running on oeis4.)