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 A381238 #17 Mar 18 2025 12:57:09 %S A381238 1,3,1,4,66,1,11,4,8,3,1,6,1,143,2,1,481,10,14,6,1,4,11,2,1,140,3,1,3, %T A381238 1,7,14,2,2,1,3,1,39,3,1,2159,3,1,4,3,1,3,1,14,10,1,11,6,1,3,1,4,185, %U A381238 1,3,1,4,78,1,3,1,6,1,4,3,2,2,1,11,17,8,15,1,16,5,1,14,4,8,7,1,20,7,96,14,62,1,3,2,2,1,91,1,10,97,1 %N A381238 a(n) = floor(b(n)), where b(n) = sec^2(b(n-1)), b(0)=1. %C A381238 a(0)-a(100) were computed using Maple with 10000 digits of precision. %C A381238 A variant of A000319 (note that sec(x)^2 is the derivative of tan(x)). %C A381238 Conjecture: Every nonnegative number appears in this sequence. (See A382148.) %H A381238 Paolo Xausa, <a href="/A381238/b381238.txt">Table of n, a(n) for n = 0..1000</a> %t A381238 Floor[NestList[Sec[#]^2 &, 1, 100]] (* _Paolo Xausa_, Mar 18 2025 *) %Y A381238 Cf. A000319, A005699, A382148. %K A381238 nonn %O A381238 0,2 %A A381238 _N. J. A. Sloane_, Mar 17 2025