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 A367897 #21 Jan 21 2024 09:16:49 %S A367897 1,2,3,6,729 %N A367897 a(1)=1, a(n) = H_(n-2)(a(n-2), a(n-1)) where H_n is the n-th hyperoperator. %C A367897 The sequence follows the hierarchy of arithmetic operations (successorship, addition, multiplication, exponentiation, tetration, ...) with the recurrence a(n-2)?a(n-1)=a(n), where "?" follows the sequence of S (successor), +, *, ^, ^^ (tetration), ... %C A367897 a(6) (=6^^729) is too large to be represented. %C A367897 Essentially a Fibonacci generalization: the Fibonacci hyperoperation sequence starting with 1. %H A367897 Wikipedia, <a href="https://en.wikipedia.org/wiki/Binary_operation">Binary operation</a> %H A367897 Wikipedia, <a href="https://en.wikipedia.org/wiki/Hyperoperation">Hyperoperation</a> %H A367897 Wikipedia, <a href="https://en.wikipedia.org/wiki/Generalizations_of_Fibonacci_numbers">Generalizations of Fibonacci numbers</a> %e A367897 a(1)=1, a(2)=S(a(1)), a(3)=a(1)+a(2), a(4)=a(2)*a(3), a(5)=a(3)^a(4), a(6)=a(4)^^a(5), ...a(1) = 1 %e A367897 a(2) = H_0(a(1), a(1)) = 1 + 1 = 2 (successor of 1 = 2) %e A367897 a(3) = H_1(a(1), a(2)) = 1 + 2 = 3 %e A367897 a(4) = H_2(a(2), a(3)) = 2 * 3 = 6 %e A367897 a(5) = H_3(a(3), a(4)) = 3^6 = 729 %Y A367897 Cf. A054871. %K A367897 nonn %O A367897 1,2 %A A367897 _Peter Woodward_, Dec 04 2023