From: utzoo!decvax!pur-ee!uiucdcs!kolstad Newsgroups: net.math Title: Rep-unit numbers of length 6k-1 - from a notesfile Article-I.D.: uiucdcs.124 Posted: Thu May 13 10:33:32 1982 Received: Fri May 14 05:27:00 1982 Reply-To: \s #N:uiucdcs:10300001:000:373 uiucdcs!kolstad May 13 10:29:00 1982 My colleague recently asked me the following question: Are all decimal numbers of length 6k-1 (k>0) consisting of all 1's composite? (e.g., 11111 = 41*271; 11111111111 = 21649 * 513239). I have deduced a general function for the numbers: 6k-1 10 - 1 f(k) = ----------- 9 but this has helped me not. Anyone got any suggestions?