A137782 - cp's OEIS frontend

A137782 a(n) = the number of permutations (p(1), p(2), ..., p(n)) of (1,2,...,n) where, for each k (2 <= k <= n), the sign of (p(k) - p(k-1)) equals the sign of (p(n+2-k) - p(n+1-k)).

n	a(n)
0	1
1	1
2	2
3	2
4	12
5	24
6	200
7	540
8	6160
9	21616
10	306432
11	1310880
12	22338624
13	113017696
14	2245983168
15	13108918368
16	297761967360
17	1969736890624
18	50332737128960
19	372125016868608
20	10565549532009472
21	86337114225206784
22	2696451226217269248
23	24132714802787013632

[1, 1, 2, 2, 12, 24, 200, 540, 6160, 21616, 306432, 1310880, 22338624, 113017696, 2245983168, 13108918368, 297761967360, 1969736890624, 50332737128960, 372125016868608, 10565549532009472, 86337114225206784, 2696451226217269248, 24132714802787013632]

cp's OEIS Frontend

A137782 a(n) = the number of permutations (p(1), p(2), ..., p(n)) of (1,2,...,n) where, for each k (2 <= k <= n), the sign of (p(k) - p(k-1)) equals the sign of (p(n+2-k) - p(n+1-k)).

Table of values

List of values