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 A242181 #17 Feb 16 2025 08:33:22
%S A242181 39,89,139,189,239,289,339,389,439,489,539,589,639,689,739,789,839,
%T A242181 889,939,989,1039,1089,1139,1189,1239,1289,1339,1389,1439,1489,1539,
%U A242181 1589,1639,1689,1739,1789,1839,1889,1939,1989,2039,2089,2139,2189,2239,2289,2339
%N A242181 Numbers with four X's in Roman numerals.
%C A242181 All these end in XXXIX.
%H A242181 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/RomanNumerals.html">Roman Numerals</a>
%H A242181 Wikipedia, <a href="http://en.wikipedia.org/wiki/Roman_numerals">Roman numerals</a>
%H A242181 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A242181 a(n) = 50n - 11. - _Charles R Greathouse IV_, May 06 2014
%e A242181 39 = XXXIX; 89 = LXXXIX.
%p A242181 A242181:=n->50*n-11; seq(A242181(n), n=1..50); # _Wesley Ivan Hurt_, May 07 2014
%p A242181 [seq(convert(50*n-11, roman), n=1..50)]; # for the Roman version - _Wolfdieter Lang_, May 09 2014
%t A242181 Table[50 n - 11, {n, 50}] (* _Wesley Ivan Hurt_, May 07 2014 *)
%o A242181 (PARI) a(n)=50*n-11 \\ _Charles R Greathouse IV_, May 06 2014
%Y A242181 Cf. A006968.
%K A242181 nonn,base,easy
%O A242181 1,1
%A A242181 _J. Lowell_, May 06 2014
%E A242181 More terms from _Wesley Ivan Hurt_, May 07 2014