A330032 The number of chains of strictly rooted upper triangular or lower triangular matrices of order n.

1, 2, 26, 9366, 204495126, 460566381955706, 12595124129900132067036747870669270, 288398561903310939256721956218813835167026180310, 2510964964470962082968627390938311899485883615067802615950711482

Offset

0,2

Comments

Also, the number of chains in the power set of (n^2-n)/2-elements such that the first term of the chains is either an empty set or a set of (n^2-n)/2-elements.

The number of rooted chains of 2-element subsets of {0,1, 2, ..., n} that contain no consecutive integers.

The number of distinct rooted reflexive symmetric fuzzy matrices of order n.

The number of chains in the set consisting of all n X n reflexive symmetric matrices such that the first term of the chains is either reflexive symmetric matrix or unit matrix.

Links

Table of n, a(n) for n=0..8.

S. R. Kannan and Rajesh Kumar Mohapatra, Counting the Number of Non-Equivalent Classes of Fuzzy Matrices Using Combinatorial Techniques, arXiv preprint arXiv:1909.13678 [math.GM], 2019.

R. B. Nelsen and H. Schmidt, Jr., Chains in power sets, Math. Mag., 64 (1) (1991), 23-31.

M. Tărnăuceanu, The number of chains of subgroups of a finite elementary abelian p-group, arXiv preprint arXiv:1506.08298 [math.GR], 2015.

Formula

a(n) = A000629((n^2-n)/2).

Crossrefs

Cf. A000629, A038719, A007047, A328044, A330301, A330302, A330804, A331957.

Sequence in context: A318132 A134795 A268667 * A273381 A094680 A259326

Adjacent sequences: A330029 A330030 A330031 * A330033 A330034 A330035

Keyword

nonn

Author

S. R. Kannan, Rajesh Kumar Mohapatra, Feb 29 2020

Status

approved