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 A005991 Let k(m) denote the least integer such that every m X m (0,1)-matrix with exactly k(m) ones in each row and in each column contains a 2 X 2 submatrix without zeros. The sequence gives the index n of the last term in each string of equal entries in the {k(m)} sequence (see A155934). (Formerly M1582) 2
 2, 6, 12, 20, 30, 43 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS E. T. Wang and R. K. Guy, Problem E2429, Amer. Math. Monthly, 81 (1974), 1112-1113. FORMULA a(n) = A003509(n + 1) - 1. - Sean A. Irvine, Jun 04 2015 EXAMPLE Since k(2) = 2 then a(1) = 2 Since k(3) = k(4) = k(5) = k(6) = 3 then a(2) = 6 Since k(7) = k(8) = ... = k(12) = 4 then a(3) = 12 Since k(13) = k(14) = ... = k(20) = 5 then a(4) = 20 Since k(21) = k(22) = ... = k(30) = 6 then a(5) = 30 Since k(31) = k(32) = ... = k(43) = 7 then a(6) = 43 CROSSREFS Cf. A003509 (index of first term), A155934. Sequence in context: A103505 A279019 A002378 * A266194 A194110 A291876 Adjacent sequences:  A005988 A005989 A005990 * A005992 A005993 A005994 KEYWORD nonn,more AUTHOR EXTENSIONS Edited by Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 02 2008 STATUS approved

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Last modified October 16 11:35 EDT 2018. Contains 316263 sequences. (Running on oeis4.)