A213430 - OEIS

A213430

The number of n X n upper triangular (0,1)-matrices M with all diagonal entries 1 such that M = f(M^2) and sum(row 1) >= sum(row 2) >= ... >= sum(row n-1) >= sum(row n) = 1 and f maps any nonzero entry to 1.
(Formerly N0663)

1, 2, 6, 26, 159, 1347, 15593, 244173, 5131436

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OFFSET

1,2

COMMENTS

A006455 is equivalent to this sequence without the nonincreasing condition on the row sums. - Petros Hadjicostas, Jul 20 2024

REFERENCES

Collected papers of Professor Hansraj Gupta. Edited by R. J. Hans-Gill and Madhu Raka. Ramanujan Mathematical Society Collected Works Series, 3. See pp. 554-564.

Hansraj Gupta, Number of topologies in a finite set, Research Bulletin of the Panjab University, Vol. 19 (1968), p. 240. MR0268836.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

LINKS

Table of n, a(n) for n=1..9.

Hansraj Gupta, Number of topologies in a finite set, Research Bulletin of the Panjab University, Vol. 19 (1968), p. 240. MR0268836.

Sean A. Irvine, Java program

Wikipedia, Finite topological space.

zbMATH, Review of Gupta article.

CROSSREFS

Cf. A000798, A001035, A006455.

Sequence in context: A099760 A112934 A135922 * A103367 A047863 A180349

Adjacent sequences: A213427 A213428 A213429 * A213431 A213432 A213433