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 A193407 #19 Aug 03 2022 02:34:37 %S A193407 1,2,3,4,5,6,7,8,9,121,131,141,151,161,171,181,191,232,242,252,262, %T A193407 272,282,292,343,353,363,373,383,393,454,464,474,484,494,565,575,585, %U A193407 595,676,686,696,787,797,898,1231,1241,1251,1261,1271,1281,1291,1321 %N A193407 Mountain numbers (version 2). %C A193407 Another version of mountain numbers (A134941). %C A193407 For n > 9 the structure of digits represents a mountain. The first digit is equal to the last digit (1 - 9). The first digits are in increasing order. The last digits are in decreasing order. The numbers only have one largest digit. This sequence is finite. The final term is 12345678987654321. %e A193407 Illustration using the member of this sequence - number 56789765: %e A193407 . . . . 9 . . . %e A193407 . . . 8 . . . . %e A193407 . . 7 . . 7 . . %e A193407 . 6 . . . . 6 . %e A193407 5 . . . . . . 5 %Y A193407 Supersequence of mountain numbers (A134941) and Giza numbers (A134810). Subsequence of hill numbers (A193408). %K A193407 nonn,base,fini %O A193407 1,2 %A A193407 _Jaroslav Krizek_, Jul 25 2011