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 A064509 Marks (in fathoms) on lead line used by ships on the Mississippi River. 0
 2, 3, 5, 7, 10, 13, 15, 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Certain depths have (or had) a visual and tactile indicator at positions on the lead line. All depths with such attachments are "marks". All others are "deeps." A leadsman measuring 12 feet of water calls "by the mark two (or twain)." If the depth on the lead is 36 feet (6 fathoms) he would call "by the deep six!". Samuel Clemens chose the nom de plume Mark Twain because, for a riverboat skipper on the Mississippi, when the water was 12 feet deep, it was safe sailing for those boats. REFERENCES Bowditch, The American Practical Navigator, 1931 edition. Postings to newsgroup rec.org.sca, circa Oct 22, 1994 by djheydt(AT)uclink.berkeley.edu (Dorothy J. Heydt), Jeff Suzuki (jeffs(AT)math.bu.EDU) and Hal Ravn. LINKS Table of n, a(n) for n=1..56. Mark S. Harris, Period measures and cautions for recipes. FORMULA For n >= 9, a(n) = 5(n-5). CROSSREFS Sequence in context: A117952 A090420 A162999 * A096221 A258084 A120367 Adjacent sequences: A064506 A064507 A064508 * A064510 A064511 A064512 KEYWORD nonn,nice AUTHOR Peter Shor, Oct 06 2001 EXTENSIONS a(55)-a(56) corrected by Sean A. Irvine, Jul 14 2023 STATUS approved

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Last modified February 29 10:20 EST 2024. Contains 370418 sequences. (Running on oeis4.)