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 A193307 #9 Sep 21 2017 03:48:30 %S A193307 0,1,-1,1,-1,1,-1,1,-1,1,-1,-1,2,15,-1,1,-1,1,-1,-1,-1,1,-1,-1,-1,3, %T A193307 -1,1,-1,3,-1,1,-1,1,-1,3,2,-1,-1,15,-1,-1,-1,-1,-1,1,-1,3,-1,-1,-1,1, %U A193307 -1,7,2,-1,2,-1,-1,-1,-1,-1,-1,1,14,1,-1,-1,6,-1,-1 %N A193307 Number of 'Reverse and Subtract' steps needed to reach 0, or -1 if never reaches 0, using base -1+i and subtracting the original number from the reversed. %H A193307 Kerry Mitchell, <a href="/A193307/b193307.txt">Table of n, a(n) for n = 0..10000</a> %H A193307 W. J. Gilbert, <a href="https://www.maa.org/programs/faculty-and-departments/classroom-capsules-and-notes/arithmetic-in-complex-bases">Arithmetic in Complex Bases</a>, Mathematics Magazine, Vol. 57, No. 2 (Mar., 1984), pp. 77-81. %e A193307 Decimal 12 is 1100 in binary, which is 2+0i using complex base -1+i. Reversing 1100 gives 0011, or 0+i. Subtracting the original number from the reversed results in -2+i, or 11111 using the complex base. Its reversal is the same, so subtracting them gives 0. Decimal 12 took 2 steps to reach 0, so a(12) = 2. %Y A193307 Cf. A193239 (number of steps needed to reach a palindrome with complex base -1+i). %Y A193307 Cf. A193306 (number of 'Reverse and Subtract' steps needed to reach 0, or -1 if never reaches 0, using base -1+i and subtracting the reversed number from the original). %K A193307 sign,base %O A193307 0,13 %A A193307 _Kerry Mitchell_, Jul 22 2011