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 A383273 #16 Apr 29 2025 13:35:50 %S A383273 1,1,2,0,2,1,0,0,12,4,0,0,45,116,44,0,0,232,1565,3005,1084,0,0,1627, %T A383273 34114,166556,249494,91192,0,0,21547 %N A383273 Triangle read by rows: T(n,k) is the number of ruler-and-compass constructions consisting of n-k lines and k circles with 0 <= k <= n. %C A383273 Row sums are given by A383082. %H A383273 Peter Kagey, <a href="https://oeis.org/A383082/a383082.png">Illustration of T(3,2) = 12 and T(3,3) = 4</a>. %F A383273 T(n,n) = A383083(n). %e A383273 n\k | 0 1 2 3 4 5 %e A383273 ----+-------------------------- %e A383273 0 | 1 %e A383273 1 | 1 2 %e A383273 2 | 0 2 1 %e A383273 3 | 0 0 12 4 %e A383273 4 | 0 0 45 116 44 %e A383273 5 | 0 0 232 1565 3005 1084 %e A383273 6 | 0 0 1627 34114 166556 249494 91192 %e A383273 T(2,1) = 2 because there are two ruler-and-compass constructions with a line and a circle: %e A383273 A circle centered at (0,0) through (1,0) and a line through (0,0),(1,0). %e A383273 A circle centered at (1,0) through (0,0) and a line through (0,0),(1,0). %e A383273 T(2,2) = 1 because there is one ruler-and-compass construction with two circles: %e A383273 A circle centered at (0,0) through (1,0) and a circle centered at (1,0) through (0,0). %Y A383273 Cf. A333944, A383082, A383083. %K A383273 nonn,tabl,hard,more %O A383273 0,3 %A A383273 _Peter Kagey_, Apr 21 2025