cp's OEIS Frontend

A190824 Number of permutations of 2 copies of 1..n introduced in order 1..n with no element equal to another within a distance of 3.

%I A190824 #25 Oct 26 2017 03:34:26
%S A190824 1,0,0,0,1,20,292,4317,69862,1251584,24728326,535333713,12616277612,
%T A190824 321762301156,8833356675295,259803215904436,8151872288855008,
%U A190824 271848098526643604,9602477503845334715,358185069617609239664,14070369448248794118128,580623906507508489287367
%N A190824 Number of permutations of 2 copies of 1..n introduced in order 1..n with no element equal to another within a distance of 3.
%H A190824 Alois P. Heinz, <a href="/A190824/b190824.txt">Table of n, a(n) for n = 0..404</a>
%H A190824 Vaclav Kotesovec, <a href="/A190824/a190824.txt">Recurrence (of order 12)</a>
%H A190824 Everett Sullivan, <a href="https://arxiv.org/abs/1611.02771">Linear chord diagrams with long chords</a>, arXiv preprint arXiv:1611.02771 [math.CO], 2016.
%F A190824 a(n) ~ 2^(n + 1/2) * n^n / exp(n+3). - _Vaclav Kotesovec_, Oct 26 2017
%e A190824 Some solutions for n=5
%e A190824 ..1....1....1....1....1....1....1....1....1....1....1....1....1....1....1....1
%e A190824 ..2....2....2....2....2....2....2....2....2....2....2....2....2....2....2....2
%e A190824 ..3....3....3....3....3....3....3....3....3....3....3....3....3....3....3....3
%e A190824 ..4....4....4....4....4....4....4....4....4....4....4....4....4....4....4....4
%e A190824 ..5....5....5....1....5....5....1....5....5....5....5....5....1....5....5....5
%e A190824 ..2....1....2....5....1....1....5....1....1....1....2....2....5....1....2....2
%e A190824 ..3....3....3....3....3....2....2....2....3....2....3....3....2....3....1....1
%e A190824 ..4....4....1....4....4....3....4....4....2....3....1....4....3....2....3....3
%e A190824 ..1....5....5....2....2....4....3....3....5....5....4....5....4....4....4....5
%e A190824 ..5....2....4....5....5....5....5....5....4....4....5....1....5....5....5....4
%Y A190824 Column k=4 of A293157.
%K A190824 nonn
%O A190824 0,6
%A A190824 _R. H. Hardin_, May 21 2011
%E A190824 a(0)=1 prepended and a(15)-a(21) added by _Alois P. Heinz_, Oct 17 2017