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 A279214 Number of permutations sigma such that |sigma(i+1)-sigma(i)| >= 3 for 1 <= i <= n - 1 and |sigma(i+2)-sigma(i)| >= 3 for 1 <= i <= n - 2. 4
 1, 1, 0, 0, 0, 0, 0, 0, 0, 2, 40, 792, 15374, 281434, 5089060, 93082532, 1743601076, 33694028152 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,10 COMMENTS 2 | a(n) for n > 1. LINKS EXAMPLE a(9) = 2: 369258147, 741852963. PROG (Ruby) def check(d, a, i)   return true if i == 0   j = 1   d_max = [i, d - 1].min   while (a[i] - a[i - j]).abs >= d && j < d_max     j += 1   end   (a[i] - a[i - j]).abs >= d end def solve(d, len, a = [])   b = []   if a.size == len     b << a   else     (1..len).each{|m|       s = a.size       if s == 0 || (s > 0 && !a.include?(m))         if check(d, a + [m], s)           b += solve(d, len, a + [m])         end       end     }   end   b end def A279214(n)   (0..n).map{|i| solve(3, i).size} end p A279214(12) CROSSREFS Cf. A002464 (|sigma(i+1)-sigma(i)| >= 2), A127697 (|sigma(i+1)-sigma(i)| >= 3). Sequence in context: A127186 A139747 A230133 * A264716 A264713 A012637 Adjacent sequences:  A279211 A279212 A279213 * A279215 A279216 A279217 KEYWORD nonn,more AUTHOR Seiichi Manyama, Dec 17 2016 EXTENSIONS a(0)-a(2), a(15)-a(17) from Alois P. Heinz, Dec 01 2018 STATUS approved

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Last modified April 3 15:00 EDT 2020. Contains 333197 sequences. (Running on oeis4.)