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 A086441 Number of inequivalent ways a semi-infinite curve can cross a straight line n times. 2
 1, 1, 2, 4, 11, 27, 79, 213, 644, 1840, 5660 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS This uses a too broad notion of equivalence. Besides the obvious reflection in a plane perpendicular to the straight line, if the end of the curve is in a free region of the plane, it is extended to infinity and the direction of the curve can then be reversed. A000560 uses a better definition of equivalence. LINKS EXAMPLE The a(3) = 2 solutions with 3 crossings. The line is drawn horizontally. The curve starts at oo and ends at X. The crossings are indicated by stars. -- X / \ / -----*----*----*---- / \ / / -- / oo --- / \ / X \ / | \ -----*----*----*---- / | / / .--- / oo CROSSREFS Isomorphism classes (using too generous a definition of isomorphism) from A000682. Cf. A000560, A001011. Sequence in context: A071314 A309886 A123441 * A316696 A319616 A148130 Adjacent sequences: A086438 A086439 A086440 * A086442 A086443 A086444 KEYWORD nonn,more AUTHOR N. J. A. Sloane, Sep 09 2003 STATUS approved

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Last modified February 8 23:03 EST 2023. Contains 360153 sequences. (Running on oeis4.)