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 A326702 #5 Jul 27 2019 14:57:51
%S A326702 0,1,1,2,2,2,2,2,1,2,2,3,3,3,3,3,2,2,3,3,3,3,3,3,2,2,3,3,3,3,3,3,2,3,
%T A326702 2,3,3,3,3,3,2,3,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
%U A326702 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3
%N A326702 Number of distinct vertices in the set-system with BII-number n.
%C A326702 A binary index of n is any position of a 1 in its reversed binary expansion. We define the set-system with BII-number n to be obtained by taking the binary indices of each binary index of n. For example, 18 has reversed binary expansion (0,1,0,0,1), and since the binary indices of 2 and 5 are {2} and {1,3} respectively, the BII-number of {{2},{1,3}} is 18.
%e A326702 The BII-number of {{1,2},{1,4}} is 260, with distinct vertices {1,2,4}, so a(260) = 3.
%t A326702 bpe[n_]:=Join@@Position[Reverse[IntegerDigits[n,2]],1];
%t A326702 Table[Length[Union@@bpe/@bpe[n]],{n,0,100}]
%Y A326702 Positions of first appearances are A072639.
%Y A326702 Cf. A000120, A029931, A048793, A070939, A326031, A326701, A326703, A326704.
%K A326702 nonn
%O A326702 0,4
%A A326702 _Gus Wiseman_, Jul 22 2019