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 A285511 #17 Apr 20 2017 12:37:21 %S A285511 9,243,6327,256,22,581,15115,392999,258,24,633,16467,428151,16480,646, %T A285511 16805,436939,11360423,16482,648,16857,438291,11395575,438304,16870, %U A285511 438629,11404363,296513447,438306,16872,438681,11405715,296548599,11405728,438694,11406053,296557387,7710492071,11405730,636 %N A285511 Value of the n-th Roman number interpreted as Latin alphabetic number. %C A285511 Lists can be numbered using different counter styles, for example using the Latin alphabet A, B, C, ..., Z, AA, AB, ... or the Roman number system I, II, III, IV, V, VI, ... Both these counter styles are defined in CSS Counter Styles Level 3 as "upper-alpha" and "upper-roman". Roman number representations are defined for the range 1 to 3999 only. Roman numerals are a subset of Latin alphabet letters; for every Roman number there is exactly one alphabetic number that looks identical. Denote the n-th Roman number by R(n) and the m-th alphabetic number by L(m), then R(n) and L(a(n)) look identical. %H A285511 Martin Janecke, <a href="/A285511/b285511.txt">Table of n, a(n) for n = 1..3999</a> %H A285511 Tab Atkins Jr. et al., <a href="https://www.w3.org/TR/2015/CR-css-counter-styles-3-20150611/">CSS Counter Styles Level 3 (W3C Candidate Recommendation)</a>, 11 June 2015 %H A285511 Martin Janecke, <a href="https://prlbr.de/2017/roman-alpha-counter-conversion/">Roman numbers ↔ Latin alphabet counter</a>, April 2017 %e A285511 The number n = 1 is written "I" in the Roman number system. "I" being the ninth letter in the alphabet is also the ninth number in the alphabetic number system. Therefore a(1) = 9. %e A285511 The number n = 2 is written "II" in the Roman number system. "II" is also the 243rd number in the alphabetic number system, because "I" is the ninth letter in the 26-letter alphabet and 9*26^1+9*26^0 = 243. Therefore a(2) = 243. %e A285511 The number n = 3 is written "III" in the Roman number system. "III" is also the 6327th number in the alphabetic number system because "I" is the ninth letter in the 26-letter alphabet and 9*26^2+9*26^1+9*26^0 = 6327. Therefore a(3) = 6327. %e A285511 The number n = 4 is written "IV" in the Roman number system. "IV" is also the 256th number in the alphabetic number system because "I" is the ninth letter in the 26-letter alphabet and "V" is the 22nd letter, therefore a(4) = 9*26^1 + 22 = 256. %e A285511 The number n = 600 is written "DC" in the Roman number system. "DC" is also the 107th number in the alphabetic number system, because "D" and "C" are the fourth and third letters in the 26-letter alphabet and 4*26^1+3*26^0 = 107. Therefore a(600) = 107. %Y A285511 Cf. A006968, A009970, A061493. %K A285511 nonn,base,easy,fini,full %O A285511 1,1 %A A285511 _Martin Janecke_, Apr 20 2017