This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A086441 #9 Apr 16 2021 00:13:51 %S A086441 1,1,2,4,11,27,79,213,644,1840,5660 %N A086441 Number of inequivalent ways a semi-infinite curve can cross a straight line n times. %C A086441 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. %H A086441 <a href="/index/Fo#fold">Index entries for sequences obtained by enumerating foldings</a> %e A086441 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. %e A086441 -- X %e A086441 / \ / %e A086441 -----*----*----*---- %e A086441 / \ / %e A086441 / -- %e A086441 / %e A086441 oo %e A086441 --- %e A086441 / \ %e A086441 / X \ %e A086441 / | \ %e A086441 -----*----*----*---- %e A086441 / | / %e A086441 / .--- %e A086441 / %e A086441 oo %Y A086441 Isomorphism classes (using too generous a definition of isomorphism) from A000682. Cf. A000560, A001011. %K A086441 nonn,more %O A086441 1,3 %A A086441 _N. J. A. Sloane_, Sep 09 2003