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 A102492 #15 Mar 17 2025 06:42:25 %S A102492 10,11,12,13,14,15,16,17,18,19,30,31,32,33,34,35,36,37,38,39,50,51,52, %T A102492 53,54,55,56,57,58,59,70,71,72,73,74,75,76,77,78,79,90,91,92,93,94,95, %U A102492 96,97,98,99,110,111,112,113,114,115,116,117,118,119,130,131,132,133 %N A102492 Numbers in base-20 representation that cannot be written with decimal digits. %H A102492 Reinhard Zumkeller, <a href="/A102492/b102492.txt">Table of n, a(n) for n = 1..10000</a> %H A102492 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Vigesimal.html">Vigesimal</a> %H A102492 Wikipedia, <a href="http://en.wikipedia.org/wiki/Vigesimal">Vigesimal</a> %e A102492 112 = 5*20^1 + 12*20^0 = '5C', therefore 112 is a term. %t A102492 Select[Range[150],Max[IntegerDigits[#,20]]>9&] (* _Harvey P. Dale_, Mar 27 2021 *) %o A102492 (Haskell) %o A102492 import Data.List (unfoldr) %o A102492 a102492 n = a102492_list !! (n-1) %o A102492 a102492_list = filter (any (> 9) . unfoldr %o A102492 (\x -> if x == 0 then Nothing else Just $ swap $ divMod x 20)) [0..] %o A102492 -- _Reinhard Zumkeller_, Jun 27 2013 %Y A102492 Complement of A102491; A102488, A102490, A102494. %K A102492 nonn,base %O A102492 1,1 %A A102492 _Reinhard Zumkeller_, Jan 12 2005