A321434 Triangle read by rows; T(n,k) is the number of achiral rows of n colors using exactly k colors.

1, 0, 1, 0, 1, 0, 1, 2, 0, 1, 2, 0, 1, 6, 6, 0, 1, 6, 6, 0, 1, 14, 36, 24, 0, 1, 14, 36, 24, 0, 1, 30, 150, 240, 120, 0, 1, 30, 150, 240, 120, 0, 1, 62, 540, 1560, 1800, 720, 0, 1, 62, 540, 1560, 1800, 720, 0, 1, 126, 1806, 8400, 16800, 15120, 5040, 0, 1, 126, 1806, 8400, 16800, 15120, 5040

Offset

0,8

Comments

Each zero in the data is the beginning of a new row.

Same as A131689, with rows (except for the first) repeated. - Joerg Arndt, Sep 08 2019

Links

Table of n, a(n) for n=0..70.

Formula

T(n,k) = k!*S2(ceiling(n/2),k), where S2 is the Stirling subset number A008277.

Example

The triangle begins with T(0,0):
1
0 1
0 1
0 1   2
0 1   2
0 1   6     6
0 1   6     6
0 1  14    36     24
0 1  14    36     24
0 1  30   150    240    120
0 1  30   150    240    120
0 1  62   540   1560   1800    720
0 1  62   540   1560   1800    720
0 1 126  1806   8400  16800   15120    5040
0 1 126  1806   8400  16800   15120    5040
0 1 254  5796  40824 126000  191520  141120   40320
0 1 254  5796  40824 126000  191520  141120   40320
0 1 510 18150 186480 834120 1905120 2328480 1451520 362880
For T(7,2)=14, the rows are AAABAAA, AABABAA, AABBBAA, ABAAABA, ABABABA, ABBABBA, ABBBBBA, BAAAAAB, BAABAAB, BABABAB, BABBBAB, BBAAABB, BBABABB, and BBBABBB.

Mathematica

Table[k! StirlingS2[Ceiling[n/2], k], {n, 0, 18}, {k, 0, (n+1)/2}] // Flatten

Crossrefs

Columns 0-6 are A000007, A057427, A056453, A056454, A056455, A056456, A056457.

Cf. A019538 (oriented), A305621 (unoriented), A305622 (chiral).

Cf. A131689.

Sequence in context: A096397 A337547 A291969 * A103919 A263234 A264394

Adjacent sequences: A321431 A321432 A321433 * A321435 A321436 A321437

Keyword

nonn,easy,tabf

Author

Robert A. Russell, Nov 09 2018

Status

approved