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 A333554 #24 May 04 2020 00:23:34 %S A333554 9,22599,782534990456559999, %T A333554 1124958024440103533642098279435875957333450115658804731260154201599999999 %N A333554 a(0) = 9; thereafter a(n+1) = 3*a(n)^4 + 4*a(n)^3 for n >= 1. %C A333554 Proposition: a(n) ends with exactly 2^n 9's. %C A333554 The number of digits in a(n) is respectively 1, 5, 18, 73, 289, 1156, 4622, ... At each step until a(6), the number of digits of a(n+1) is nearly 4 times the number of digits of a(n), and exactly so from a(4) to a(5). %C A333554 Sequence has doubly-exponential growth: log log a(n) ~ n. - _Charles R Greathouse IV_, Mar 27 2020 %D A333554 Eric Billault, Walter Damin, Robert Ferréol et al., MPSI - Classes Prépas, Khôlles de Maths, Ellipses, 2012, exercice 4.21 pages 79 and 91. %e A333554 a(2) = 3*22599^4 + 4*22599^3 = 782534990456559999 ends with 2^2 digits 9's. %t A333554 a[0] = 9; a[n_] := a[n] = 3*a[n-1]^4 + 4*a[n-1]^3; Array[a, 4, 0] (* _Amiram Eldar_, Mar 26 2020 *) %Y A333554 Subsequence of A017377. %K A333554 nonn,base %O A333554 0,1 %A A333554 _Bernard Schott_, Mar 26 2020