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 A351413 a(n) is the maximum number of stable matchings in the Latin Stable Marriage Problem of order n. 1
 1, 2, 3, 10, 9, 48, 61 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS In the Latin Stable Marriage Problem of order n, the sum of a man and woman's rankings of each other is n+1. This implies that the men's and women's ranking tables are Latin squares. As a subproblem of the Stable Marriage Problem, Latin instances provide lower bounds for the maximum number of stable matchings in the general problem, such as A005154 and A065982. For sizes 1 to 4, Latin instances provide exact bounds; they are conjectured to provide exact bounds for sizes a power of 2; they provide the best lower bounds known for sizes 6, 10, 12, and 24, of 48, 1000, 6472, and 126112960, respectively. The next term, a(8), is conjectured to be 268, consistent with A005154. The minimum number of stable matchings for Latin instances of order n is n, and is realized for the cyclic group of order n. The average number of stable matchings is 7 for n=4 (cf. A351430 showing an average of about 1.5 for the general problem), and benefits from avoidance of mutual first choices and more generally the lack of overlap between the men's and women's preferred matchings. The Latin squares of A005154 and A065982 can be interpreted as multiplication tables of groups, n-th powers of the cyclic group C2 and n-th dihedral groups, respectively. The sequence decreases from a(4)=10 to a(5)=9, in contrast to the corresponding sequence for the general problem, which Thurber showed to be strictly increasing. This has motivated the study of less restrictive subproblems, such as pseudo-Latin squares (A069124, A069156), Latin x Latin instances (A344664, A344665, A343697), instances where participants have different first choices (A343475, A343694, A343695), or instances with unspecified/tied/template rankings (A284458 with only first choices specified). The sequence is empirically derived, originally based on reduced Latin squares (A000315). There are fewer instances to try using RC-equivalent Latin squares (A123234) instead of reduced Latin squares. REFERENCES C. Converse, Lower bounds for the maximum number of stable pairings for the general marriage problem based on the latin marriage problem, Ph. D. Thesis, Claremont Graduate School, Claremont, CA (1992) [Examples are from 69-70]. LINKS Table of n, a(n) for n=1..7. A. T. Benjamin, C. Converse, and H. A. Krieger, Note. How do I marry thee? Let me count the ways, Discrete Appl. Math. 59 (1995) 285-292. Matvey Borodin, Eric Chen, Aidan Duncan, Tanya Khovanova, Boyan Litchev, Jiahe Liu, Veronika Moroz, Matthew Qian, Rohith Raghavan, Garima Rastogi, and Michael Voigt, Sequences of the Stable Matching Problem, arXiv:2201.00645 [math.HO], 2021 [Sections 3.7 and 4.2]. J. S. Hwang, Complete stable marriages and systems of I-M preferences, In: McAvaney K.L. (eds) Combinatorial Mathematics VIII. Lecture Notes in Mathematics, vol 884. Springer, Berlin, Heidelberg (1981) 49-63. E. G. Thurber, Concerning the maximum number of stable matchings in the stable marriage problem, Discrete Math., 248 (2002), 195-219. EXAMPLE Maximal instance of order 2 with 2 stable matchings: 12 21 Maximal instance of order 3 with 3 stable matchings: 123 231 312 Maximal instance of order 4 with 10 stable matchings (group C2xC2): 1234 2143 3412 4321 Maximal instance of order 5 with 9 stable matchings: 12345 21453 34512 45231 53124 Maximal instance of order 6 with 48 stable matchings (Dihedral group): 123456 214365 365214 456123 541632 632541 Maximal instance of order 7 with 61 stable matchings: 1234567 2316745 3125476 4657312 5743621 6471253 7562134 CROSSREFS Cf. A005154 (powers of 2), A065982 (multiples of 2), A069156 (not necessarily Latin), A000315 (reduced Latin squares), A123234 (RC-equivalent Latin squares). Sequence in context: A193729 A303115 A074068 * A283436 A225558 A362089 Adjacent sequences: A351410 A351411 A351412 * A351414 A351415 A351416 KEYWORD nonn,hard,more AUTHOR Dan Eilers, Feb 10 2022 STATUS approved

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Last modified May 18 09:54 EDT 2024. Contains 372620 sequences. (Running on oeis4.)