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 A060202 #6 Jul 02 2025 16:02:01 %S A060202 4,6,12,36,180,1620,27540,908820,59073300,7620455700,1958457114900, %T A060202 1004688499943700,1029805712442292500,2110071904794257332500, %U A060202 8644964593942072291252500,70828194918167398282231732500 %N A060202 Let G = complete graph on 4 vertices, create the sequence G, L(G), L(L(G)), L(L(L(G))), ... where each graph in this sequence is the line graph of the previous graph; a(n) is number of vertices of the n-th graph in this sequence. %C A060202 If G is k-regular, then L(G) is (2k-2)-regular. From this it is easy to get the formula for a(n). %F A060202 a(0)=4 and for n >= 1 a(n) = 4 * product k=1...n (1+2^(k-2)) %e A060202 The line graph of the complete graph on 4 vertices has C(4,2) vertices so a(1) = 6. %p A060202 for n from 0 to 30 do printf(`%d,`,4*product(1+2^(k-2), k=1..n)) od: %K A060202 nonn %O A060202 0,1 %A A060202 Avi Peretz (njk(AT)netvision.net.il), Mar 18 2001 %E A060202 More terms from _James Sellers_ and _Vladeta Jovovic_, Mar 26 2001