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 A249071 #18 Nov 23 2019 04:02:53 %S A249071 0,0,1,0,1,1,1,0,1,2,2,2,2,2,1,0,1,2,2,3,3,4,4,3,4,4,3,3,2,2,1,0,1,2, %T A249071 3,3,4,4,5,5,6,6,5,6,6,7,7,6,7,7,6,6,5,6,6,5,5,4,4,3,3,2,1,0,1,2,3,3, %U A249071 4,5,5,6,7,7,8,8,8,8,8,9,9,10,10,11,11,10,11,11,12,12,11,12,12,11,11,10,11,11,12,12,11,12,12,11,11,10,11,11,10,10,9,9,8,8,8,8,8,7,7,6,5,5,4,3,3,2,1,0 %N A249071 a(n) = A004001(2*n) - n, where A004001 is Hofstadter-Conway $10000 sequence. %C A249071 Hofstadter shows the plot of function A004001(n)-(n/2) at time 10:52 during the part two of DIMACS lecture. This sequence is obtained as the bisection of that function, thus containing only integers. Cf. also A004074. %H A249071 Antti Karttunen, <a href="/A249071/b249071.txt">Table of n, a(n) for n = 1..16384</a> %H A249071 D. R. Hofstadter, Analogies and Sequences: Intertwined Patterns of Integers and Patterns of Thought Processes, Lecture in DIMACS Conference on Challenges of Identifying Integer Sequences, Rutgers University, October 10 2014; <a href="http://vimeo.com/109139374">Part 1</a>, <a href="http://vimeo.com/109139377">Part 2</a>. %H A249071 Wikipedia, <a href="http://en.wikipedia.org/wiki/Blancmange_curve">Blancmange curve</a> %H A249071 <a href="/index/Ho#Hofstadter">Index entries for Hofstadter-type sequences</a> %F A249071 a(n) = A004001(2*n) - n. %F A249071 a(n) = A004074(2*n) / 2. [Also the even bisection of A004074 halved.] %o A249071 (Scheme, two alternative versions): %o A249071 (define (A249071 n) (- (A004001 (* 2 n)) n)) %o A249071 (define (A249071 n) (/ (A004074 (* 2 n)) 2)) %Y A249071 Cf. A004001, A004074. %Y A249071 Cf. also A233270 (also has a similar Blancmange curve appearance). %K A249071 nonn %O A249071 1,10 %A A249071 _Antti Karttunen_, Oct 22 2014