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 A259471 Triangle read by rows: T(n,k) = number of out-regular relations on n points with index k (0 <= k <= n). 0
 1, 1, 1, 1, 3, 1, 1, 7, 7, 1, 1, 19, 66, 19, 1, 1, 47, 916, 916, 47, 1, 1, 130, 16816, 91212, 16816, 130, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 LINKS S. A. Choudum, K. R. Parthasarathy, Semi-regular relations and digraphs, Nederl. Akad. Wetensch. Proc. Ser. A. {75}=Indag. Math. 34 (1972), 326-334. EXAMPLE Triangle begins: 1, 1,1, 1,3,1, 1,7,7,1, 1,19,66,19,1, 1,47,916,916,47,1, 1,130,16816,91212,16816,130,1, ... CROSSREFS Columns give A001372, A003286, A005535. Sequence in context: A059328 A174387 A176791 * A220555 A075440 A137470 Adjacent sequences:  A259468 A259469 A259470 * A259472 A259473 A259474 KEYWORD nonn,tabl,more AUTHOR N. J. A. Sloane, Jul 03 2015 STATUS approved

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Last modified April 6 16:14 EDT 2020. Contains 333276 sequences. (Running on oeis4.)