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 A193412 #21 Aug 03 2022 02:34:50 %S A193412 1,2,3,4,5,6,7,8,9,101,202,212,303,313,323,404,414,424,434,505,515, %T A193412 525,535,545,606,616,626,636,646,656,707,717,727,737,747,757,767,808, %U A193412 818,828,838,848,858,868,878,909,919,929,939,949,959,969,979,989,2012 %N A193412 1..9 followed by the canyon numbers A134970. %C A193412 For n > 9 the structure of digits represents an abyss. The first digit is equal to the last digit (1 - 9). The first digits are in decreasing order. The last digits are in increasing order. The numbers only have one smallest digit. This sequence is finite. The final term is 9876543210123456789. %C A193412 Superset of crater numbers (A193409). Subset of valley numbers (A193413). %e A193412 Illustration using 654356: %e A193412 6 . . . . 6 %e A193412 . 5 . . 5 . %e A193412 . . 4 . . . %e A193412 . . . 3 . . %Y A193412 Cf. A193409, A193413, A134970. %K A193412 nonn,base,fini %O A193412 1,2 %A A193412 _Jaroslav Krizek_, Jul 25 2011