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 A055123 #12 Mar 31 2017 22:21:30 %S A055123 0,12,11,10,9,8,7,6,5,4,3,2,1,156,168,167,166,165,164,163,162,161,160, %T A055123 159,158,157,143,155,154,153,152,151,150,149,148,147,146,145,144,130, %U A055123 142,141,140,139,138,137,136,135,134,133,132,131,117,129,128,127,126 %N A055123 Base-13 complement of n (write n in base 13, then replace each digit with its base-13 negative). %H A055123 Alois P. Heinz, <a href="/A055123/b055123.txt">Table of n, a(n) for n = 0..2196</a> %H A055123 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %Y A055123 Cf. A004488, A048647, A055115-A055126. %Y A055123 Column k=13 of A248813. %K A055123 base,easy,nonn %O A055123 0,2 %A A055123 _Henry Bottomley_, Apr 19 2000