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 A308625 #32 Aug 03 2024 17:10:52 %S A308625 0,0,1,0,1,2,0,1,2,3,0,2,3,3,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, %T A308625 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1, %U A308625 1,1,1,1,1,1,1,1,1,1,1,1,1,1 %N A308625 Van Eck sequence in 2-dimensional hexagonal space. %C A308625 Fill a board made from hexagonal cells with numbers using the following rules: %C A308625 - write a 0 in the starting cell; %C A308625 - if the number just written had not previously been on the board then the next number is 0; %C A308625 - otherwise, the next number is the distance from its closest occurrence, counting cells you need to pass through to reach it. %C A308625 ______ ______ %C A308625 / \ / \ %C A308625 / \ / \ %C A308625 ______/ \______/ \______ %C A308625 / \ / \ / \ %C A308625 / \ / \ / \ %C A308625 / \______/ 2 \______/ \ %C A308625 \ / \ . . / \ / %C A308625 \ / .\ / . \ / %C A308625 \______/ 1 \______/ 3 \______/ %C A308625 / \ . / \ . / \ %C A308625 / \ . / \ / . \ %C A308625 / 1 \___.__/ 0 \______/ 0 \ %C A308625 \ . / . \ . . / \ . / %C A308625 \ . / . \ . / . \ . / %C A308625 \___.__/ 0 \___.__/ 1 \___.__/ %C A308625 / . \ . / ^ \ . / . \ %C A308625 / . \ . / | \ . / . \ %C A308625 / 1 \___.__/ 0 \___.__/ 2 \ %C A308625 \ . / . \ START / . \ . / %C A308625 \ . / . \ / . \ . / %C A308625 \___.__/ 2 \______/ 0 \___.__/ %C A308625 / . \ . / \ . / . \ %C A308625 / . \ / . .\ / . \ %C A308625 / 1 \______/ 1 \______/ 3 \ %C A308625 \ . / \ / \ . / %C A308625 \ / . \ / .\ / %C A308625 \______/ 1 \______/ 3 \______/ %C A308625 / \ . / \ . / \ %C A308625 / \ / . .\ / \ %C A308625 / \______/ 1 \______/ \ %C A308625 \ / \ / \ / %C A308625 \ / \ / \ / %C A308625 \______/ \______/ \______/ %C A308625 . %C A308625 a(n) = 1 for all n > 15, because the previous 1 will always be adjacent to another 1. - _Charlie Neder_, Jun 11 2019 %H A308625 <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (1). %F A308625 G.f.: x^3*(1 - x + x^2 + x^3 - 2*x^4 + x^5 + x^6 + x^7 - 3*x^8 + 2*x^9 + x^10 - 2*x^12)/(1 - x). - _Elmo R. Oliveira_, Aug 03 2024 %Y A308625 Cf. A181391, A308626. %K A308625 nonn,easy %O A308625 1,6 %A A308625 _Jacek Sandomierz_, Jun 11 2019 %E A308625 Extended by _Charlie Neder_, Jun 13 2019