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 A081828 #13 Feb 16 2025 08:32:48 %S A081828 1,4,7,9,10,12,13,18,20,21,22,25,27,28,29,32,41,43,44,45,46,54,59,60, %T A081828 61,82,87,90,91,92,93,94,102,111,133,154,157,163,177,182,186,187,188, %U A081828 189,190,273,334,342,350,360,367,378,379,380,381,382,418,431,441,464,483 %N A081828 Numbers n such that 2 successive terms of Hofstadter Q-sequence are the same. %C A081828 A005185(a(n)+1) = A005185(a(n)); A081827(a(n)) = 0. %H A081828 Reinhard Zumkeller, <a href="/A081828/b081828.txt">Table of n, a(n) for n = 1..250</a> %H A081828 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HofstadtersQ-Sequence.html">Hofstadter's Q-Sequence</a> %H A081828 Wikipedia, <a href="http://en.wikipedia.org/wiki/Hofstadter_sequence">Hofstadter sequence</a> %H A081828 <a href="/index/Ho#Hofstadter">Index entries for Hofstadter-type sequences</a> %o A081828 (Haskell) %o A081828 import Data.List (elemIndices) %o A081828 a081828 n = a081828_list !! (n-1) %o A081828 a081828_list = map (+ 1) $ elemIndices 0 a081827_list %o A081828 -- _Reinhard Zumkeller_, Sep 15 2011 %Y A081828 Cf. A081829, A081830, A194626. %K A081828 nonn %O A081828 1,2 %A A081828 _Benoit Cloitre_, Apr 10 2003