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 A339283 #4 Nov 30 2020 21:40:17
%S A339283 1,4,28,361,7061,184327,5941855,226973560,10011116097,500553647373,
%T A339283 27975194135702,1728193768303770,116934429186262096,
%U A339283 8600448307248025405,683181845460624644202,58290243136791332908001,5316517137637684870655592,516199318599186277653647746
%N A339283 Number of unoriented series-parallel networks with n integer valued elements spanning an initial interval of positive integers.
%C A339283 See A339282 for additional details.
%e A339283 In the following examples, elements in series are juxtaposed and elements in parallel are separated by '|'.
%e A339283 a(1) = 1: (1).
%e A339283 a(2) = 4: (11), (12), (1|1), (1|2).
%o A339283 (PARI) \\ See A339282 for R(n,k).
%o A339283 seq(n)={sum(k=1, n, R(n, k)*sum(r=k, n, binomial(r, k)*(-1)^(r-k)) )}
%Y A339283 Row sums of A339282.
%Y A339283 Cf. A339225, A339229.
%K A339283 nonn
%O A339283 1,2
%A A339283 _Andrew Howroyd_, Nov 30 2020