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 A204811 Groupless numbers. 0
 195, 205, 208, 211, 212, 214, 217, 218, 220, 227, 229, 235, 242, 244, 246, 247, 248, 252, 253, 255, 257, 258, 259, 263, 264, 265, 266, 267, 269, 271, 274, 275, 279, 283, 286, 287, 289, 290, 291, 294, 295, 297, 298 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Let [n]={1,..,n}. A number n is groupless iff there is no binary operation . on [n] such that G=([n],.) is a group, and . extends the partial graph of multiplication on [n], i.e., whenever i,j and their usual product i*j are in [n], then i.j=i*j. If n is not groupless, a witness G is sometimes called an FLP group. The term "groupless" was coined by Thomas Chartier. LINKS Andrés Eduardo Caicedo, Thomas A. C. Chartier, Péter Pál Pach, Coloring the n-smooth numbers with n colors, arXiv:1902.00446 [math.NT], 2019. Th. A. Ch. Chartier, Coloring problems, MS Thesis in Mathematics, Boise State University, December, 2011. R. Forcade and A. Pollington, What is special about 195? Groups, n-th-power maps and a problem of Graham, in Proceedings of the First Conference of the Canadian Number Theory Association, Banff, 1988, R.A. Mollin, ed., Walter de Gruyter, Berlin, 1990, 147-155. CROSSREFS Sequence in context: A183583 A296893 A045073 * A234814 A154938 A234100 Adjacent sequences:  A204808 A204809 A204810 * A204812 A204813 A204814 KEYWORD nonn AUTHOR Andres E. Caicedo, Jan 19 2012 STATUS approved

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Last modified October 14 14:45 EDT 2019. Contains 328019 sequences. (Running on oeis4.)