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 A326289 #13 Jul 27 2020 12:20:50
%S A326289 0,0,0,4,56,1008,32736,2097088,268435328,68719476480,35184372088320,
%T A326289 36028797018962944,73786976294838204416,302231454903657293672448,
%U A326289 2475880078570760549798240256,40564819207303340847894502555648,1329227995784915872903807060280311808
%N A326289 a(0) = 0, a(n) = 2^binomial(n,2) - 2^(n - 1).
%C A326289 Number of simple graphs with vertices {1..n} containing two edges {a,b}, {c,d} that are weakly crossing, meaning a <= c < b <= d or c <= a < d <= b.
%e A326289 The a(4) = 56 weakly crossing edge-sets:
%e A326289 {12,13} {12,13,14} {12,13,14,23} {12,13,14,23,24} {12,13,14,23,24,34}
%e A326289 {12,14} {12,13,23} {12,13,14,24} {12,13,14,23,34}
%e A326289 {12,23} {12,13,24} {12,13,14,34} {12,13,14,24,34}
%e A326289 {12,24} {12,13,34} {12,13,23,24} {12,13,23,24,34}
%e A326289 {12,34} {12,14,23} {12,13,23,34} {12,14,23,24,34}
%e A326289 {13,14} {12,14,24} {12,13,24,34} {13,14,23,24,34}
%e A326289 {13,23} {12,14,34} {12,14,23,24}
%e A326289 {13,24} {12,23,24} {12,14,23,34}
%e A326289 {13,34} {12,23,34} {12,14,24,34}
%e A326289 {14,24} {12,24,34} {12,23,24,34}
%e A326289 {14,34} {13,14,23} {13,14,23,24}
%e A326289 {23,24} {13,14,24} {13,14,23,34}
%e A326289 {23,34} {13,14,34} {13,14,24,34}
%e A326289 {24,34} {13,23,24} {13,23,24,34}
%e A326289 {13,23,34} {14,23,24,34}
%e A326289 {13,24,34}
%e A326289 {14,23,24}
%e A326289 {14,23,34}
%e A326289 {14,24,34}
%e A326289 {23,24,34}
%t A326289 Table[If[n==0,0,2^Binomial[n,2]-2^(n-1)],{n,0,5}]
%Y A326289 Cf. A000088, A000108, A002662, A006125, A016098, A054726, A324170.
%Y A326289 Cf. A326210, A326244, A326248, A326250, A326257, A326279, A326290.
%K A326289 nonn
%O A326289 0,4
%A A326289 _Gus Wiseman_, Jun 23 2019