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 A370199 #13 Feb 15 2024 13:28:59 %S A370199 0,1,3,11,35,108,380,1348,5014,18223,67634,252849,950346,3602437, %T A370199 13697333,52293534,200399576,770410271,2970369338,11482572252, %U A370199 44492417777,172766286339,672186167762,2619985274260,10228841840226,39996338183554,156612016049122 %N A370199 a(n) is the number of odd polyominoes with n cells. %C A370199 Whether a polyomino is "odd" is determined by the fact that the permutation defined by assigning the positions from row- or column-wise enumeration of its cells on a square grid is an odd permutation. See the description in the 'Ponder This' challenge for the exact definition. %C A370199 The terms a(1)-a(10) were given in this description, and a(11)-a(20) were in the solution. The larger terms are results of the program that the user "uau" provided in the Mersenne forum. %H A370199 IBM Research, <a href="https://research.ibm.com/haifa/ponderthis/challenges/June2022.html">Counting odd polyominoes</a>, Ponder This, June 2022 - Challenge. %H A370199 IBM Research, <a href="https://research.ibm.com/haifa/ponderthis/solutions/June2022.html">Counting odd polyominoes</a>, Ponder This, June 2022 - Solution. %H A370199 User uau, <a href="https://www.mersenneforum.org/showpost.php?p=610016&postcount=10">C program</a>, post in mersenneforum, Jul 22, 2022. %F A370199 a(4*n+2) = A001168(4*n+2)/2. %F A370199 a(4*n+3) = A001168(4*n+3)/2. %o A370199 (C) See the 'user uau' link. %Y A370199 Cf. A001168. %K A370199 nonn,hard,more %O A370199 1,3 %A A370199 _Joerg Arndt_ and _Hugo Pfoertner_, Feb 11 2024