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 A212693 Number of legal 7 X 6 Connect-Four positions after n plies. 6
 1, 7, 49, 238, 1120, 4263, 16422, 54859, 184275, 558186, 1662623, 4568683, 12236101, 30929111, 75437595, 176541259, 394591391, 858218743, 1763883894, 3568259802, 6746155945, 12673345045, 22010823988, 38263228189, 60830813459, 97266114959, 140728569039 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Sum of all 43 terms is 4531985219092 as computed by Edelkamp and Kissmann (see link). LINKS John Tromp, Table of n, a(n) for n = 0..42 (copied from the P. Kissmann link) Dennis Aanstoot, Graph rewriters as components, Univ. of Twente (Netherlands, 2022). S. Edelkamp and P. Kissmann, Symbolic Classification of General Two-Player Games Brady Haran, Connect Four, Numberphile video, 2013. Johannes Niklas Hartmann, Finding optimal strategies in sequential games with the novel selection monad, arXiv:2105.12514 [cs.AI], 2021. P. Kissmann, Algorithm Engineering - Symbolische Suche [broken link] John Tromp, John's Connect Four Playground EXAMPLE a(3) = 7 * (1*7 + 6*(5/2 + 2)) = 238 because 3 discs played in different columns can be transposed in two ways. CROSSREFS Cf. A090224 (upper bound), A013582. Sequence in context: A141783 A181479 A223842 * A223615 A188768 A188757 Adjacent sequences: A212690 A212691 A212692 * A212694 A212695 A212696 KEYWORD nonn,fini,full AUTHOR _John Tromp_, May 23 2012 STATUS approved

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Last modified March 3 21:58 EST 2024. Contains 370518 sequences. (Running on oeis4.)