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 A356121 #18 Dec 19 2024 11:46:19 %S A356121 1,4,14,49,86,301,1849,454,1589,9761,51529,886,3101,19049,100561, %T A356121 196249,3986,13951,85699,452411,882899,3972049,31754,111139,682711, %U A356121 3604079,7033511,31642861,252079129,6418,22463,137987,728443,1421587,6395537,50949293,10297681 %N A356121 Matula-Goebel number of the rooted binary tree with Colijn-Plazzotta number n. %C A356121 A permutation of A111299. %H A356121 C. Colijn and G. Plazzotta, <a href="https://doi.org/10.1093/sysbio/syx046">A Metric on Phylogenetic Tree Shapes</a>, Systematic Biology, volume 67, number 1, January 2018, pages 113-126. %H A356121 F. Goebel, <a href="https://doi.org/10.1016/0095-8956(80)90049-0">On a 1-1-Correspondence between Rooted Trees and Natural Numbers</a>, Journal of Combinatorial Theory, series B, volume 29, 1980, pages 141-143. %H A356121 D. W. Matula, <a href="https://doi.org/10.1137/1010054">A Natural Rooted Tree Enumeration By Prime Factorization</a>, SIAM Review, volume 10, number 2, April 1968, page 273 (also <a href="http://www.jstor.org/stable/2027327">at JSTOR</a>). %H A356121 Kevin Ryde, <a href="/A356121/a356121.gp.txt">PARI/GP Code</a> %H A356121 <a href="/index/Mat#matula">Index entries for sequences related to Matula-Goebel numbers</a> %F A356121 a(n) = prime(a(x)) * prime(a(y)) for n>=2, where subtrees x = A002024(n-1) and y = A002260(n-1). %o A356121 (PARI) \\ See links. %Y A356121 Cf. A002024, A002260, A111299. %K A356121 nonn %O A356121 1,2 %A A356121 _Kevin Ryde_, Jul 31 2022