A137783 - cp's OEIS frontend

A137783 a(n) = the number of permutations (p(1), p(2), ..., p(2n+1)) of (1, 2, ..., 2n+1) where, for each k (2 <= k <= 2n+1), the sign of (p(k) - p(k-1)) equals the sign of (p(2n+2-k) - p(2n+3-k)).

n	a(n)
0	1
1	4
2	44
3	1028
4	40864
5	2484032
6	214050784
7	24831582176
8	3731039384576
9	704879630525696
10	163539441616948736
11	45712130697710081024
12	15150993151215400441856
13	5875388829103413298173952
14	2635427286694074346846232576
15	1353918066433734600362650169344

[1, 4, 44, 1028, 40864, 2484032, 214050784, 24831582176, 3731039384576, 704879630525696, 163539441616948736, 45712130697710081024, 15150993151215400441856, 5875388829103413298173952, 2635427286694074346846232576, 1353918066433734600362650169344]

cp's OEIS Frontend

A137783 a(n) = the number of permutations (p(1), p(2), ..., p(2n+1)) of (1, 2, ..., 2n+1) where, for each k (2 <= k <= 2n+1), the sign of (p(k) - p(k-1)) equals the sign of (p(2n+2-k) - p(2n+3-k)).

Table of values

List of values