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 A189281 Number of permutations p of 1,2,...,n satisfying p(i+2)-p(i)<>2 for all 1<=i<=n-2. 6
 1, 1, 2, 5, 18, 75, 410, 2729, 20906, 181499, 1763490, 18943701, 222822578, 2847624899, 39282739034, 581701775369, 9202313110506, 154873904848803, 2762800622799362, 52071171437696453, 1033855049655584786, 21567640717569135515 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n) is also number of ways to place n nonattacking pieces rook + semi-leaper[2,2] on an n X n chessboard. LINKS Vaclav Kotesovec, Table of n, a(n) for n = 0..35 V. Kotesovec, Number of ways of placing non-attacking queens, kings, bishops and knights (in English and Czech) Vaclav Kotesovec, Mathematica program for this sequence FORMULA Asymptotic (V. Kotesovec, Mar 2011): a(n)/n! ~ (1 + 3/n + 2/n^2)/e. CROSSREFS Cf. A000255, A002464, A055790, A110128. Sequence in context: A039744 A319121 A289655 * A006848 A208968 A206293 Adjacent sequences:  A189278 A189279 A189280 * A189282 A189283 A189284 KEYWORD nonn,hard AUTHOR Vaclav Kotesovec, Apr 19 2011 EXTENSIONS Terms a(33)-a(35) from Vaclav Kotesovec, Apr 20 2012 STATUS approved

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Last modified March 25 04:15 EDT 2019. Contains 321457 sequences. (Running on oeis4.)