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 A362004 #15 Feb 16 2025 08:34:05 %S A362004 1,2,4,1,6,2,2 %N A362004 Initial digit of the decimal expansion of the tetration 2^^n (in Don Knuth's up-arrow notation). %C A362004 The most significant digit of the base-10 representation of 2^(2^(2^...)) n times is given by floor(2^^n/10^(len(2^^n)-1)), where len(2^^n) indicates the number of digits of the argument. %C A362004 Although it is known that 2^^6 starts with the digit 2 (see A241291), a(7) is not currently known (for details, see Googology link, section "First digits in tetration"). %H A362004 Googology, <a href="https://googology.fandom.com/wiki/Tetration">Tetration</a>. %H A362004 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PowerTower.html">Power Tower</a> %H A362004 Wikipedia, <a href="https://en.wikipedia.org/wiki/Knuth%27s_up-arrow_notation">Knuth's up-arrow notation</a> %H A362004 Wikipedia, <a href="https://en.wikipedia.org/wiki/Tetration">Tetration</a> %F A362004 a(n) = floor(2^^n/10^floor(log(2^^n))). %e A362004 a(4) = 6, since 2^^4 = 65536. %Y A362004 Cf. A241291, A241299, A244059. %K A362004 base,hard,more,nonn %O A362004 0,2 %A A362004 _Marco Ripà_, Apr 02 2023