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 A105247 #10 Feb 17 2019 18:32:36 %S A105247 1,1,1,5,5,5,5,5,10,10,10,10,10,50,50,50,50,50,100,100,100,100,100, %T A105247 500,500,500,500,500,1000,1000,1000,1000,1000,5000,5000,5000,5000, %U A105247 5000,10000,500,500,500,500,2500,2500,2500,2500,2500,5000,50,50,50,50,250 %N A105247 Product of digits of Roman Numerals. %C A105247 New Roman Numerals A006968 (i.e., 4 = IV, not IIII). Related to sum of digits of n in Roman numeral representation A093783. %H A105247 Nathaniel Johnston, <a href="/A105247/b105247.txt">Table of n, a(n) for n = 1..3999</a> %H A105247 Gerard Schildberger and Frank Ellermann, <a href="/A006968/a006968.txt">The numbers from 1 to 3999 expressed as Roman numerals</a>. %e A105247 a(3) = 1 because 3 = "III" and I*I*I = I = 1. %e A105247 a(4) = 5 because 4 = "IV" and I*V = V = 5. %e A105247 a(9) = 10 because 9 = "IX" and I*X = X = 10. %e A105247 a(14) = 50 because 14 = "XIV" and X*I*V = L = 50. %e A105247 a(19) = 100 because 19 = "XIX" and X*I*X = C = 100. %e A105247 a(24) = 500 because 24 = "XXIV" and X*X*I*V = D = 500. %e A105247 a(29) = 1000 because 29 = "XXIX" and X*X*I*X = M = 1000. %e A105247 a(34) = 5000 because 34 = "XXXIV" and X*X*X*I*V = 5000. %e A105247 a(39) = 10000 because 39 = "XXXIX" and X*X*X*I*X = myriad = 10000. %e A105247 a(40) = 500 because 40 = "XL" and X*L = D = 500. %e A105247 a(44) = 2500 because 44 = "XLIV" and X*L*I*V = MMD = 2500. %e A105247 a(49) = 5000 because 49 = "XLIX" and X*L*I*X = 5000. %e A105247 a(50) = 50 because 50 = L. %p A105247 with(StringTools): A105247 := proc(n) local r: r:=convert(n, roman): return mul(parse(SubstituteAll( SubstituteAll( SubstituteAll( SubstituteAll( SubstituteAll( SubstituteAll( SubstituteAll(r[j], "I", "1"), "V", "5"), "X", "10"), "L", "50"), "C", "100"), "D", "500"), "M", "1000")),j=1..length(r)): end: seq(A105247(n),n=1..54); # _Nathaniel Johnston_, May 18 2011 %Y A105247 Cf. A006968, A093783. %K A105247 base,easy,fini,nonn %O A105247 1,4 %A A105247 _Jonathan Vos Post_, Apr 14 2005