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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.

A202341 Numbers occurring exactly once in Hofstadter H-sequence A005374.

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%I A202341 #18 Mar 09 2025 13:05:38
%S A202341 0,2,3,6,8,9,11,12,15,16,19,21,22,25,27,28,30,31,34,36,37,39,40,43,44,
%T A202341 47,49,50,52,53,56,57,60,62,63,66,68,69,71,72,75,76,79,81,82,85,87,88,
%U A202341 90,91,94,96,97,99,100,103,104,107,109,110,113,115,116,118
%N A202341 Numbers occurring exactly once in Hofstadter H-sequence A005374.
%C A202341 A202340(a(n)) = 1.
%H A202341 Reinhard Zumkeller, <a href="/A202341/b202341.txt">Table of n, a(n) for n = 1..10000</a>
%H A202341 Jeffrey Shallit, <a href="https://arxiv.org/abs/2503.01026">The Narayana Morphism and Related Words</a>, arXiv:2503.01026 [math.CO], 2025.
%H A202341 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HofstadterH-Sequence.html">Hofstadter H-Sequence</a>.
%H A202341 Wikipedia, <a href="http://en.wikipedia.org/wiki/Hofstadter_sequence">Hofstadter sequence</a>.
%H A202341 <a href="/index/Ho#Hofstadter">Index entries for Hofstadter-type sequences</a>.
%o A202341 (Haskell)
%o A202341 import Data.List (elemIndices)
%o A202341 a202341 n = a202341_list !! (n-1)
%o A202341 a202341_list = elemIndices 1 a202340_list
%Y A202341 Cf. A005374, A202340, A202342 (complement).
%K A202341 nonn
%O A202341 1,2
%A A202341 _Reinhard Zumkeller_, Dec 17 2011