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 A171865 #18 May 22 2025 10:21:35 %S A171865 1,2,4,6,11,13,18,21,25,31,36,42,45,48,53,57,60,64,67,73,82,85,90,93, %T A171865 99,102,106,111,117,122,126,130,135,139,143,149,153,157,163,169,174, %U A171865 180,184,188,197,200,203,209,213,216,226,229,233,237,243,247,252,255,258,264,270 %N A171865 Positions of 0's in A181391. %C A171865 A181391(a(n)) = 0; the sequence is infinite, proof by Jan Ritsema van Eck in comments in A181391. %H A171865 Reinhard Zumkeller, <a href="/A171865/b171865.txt">Table of n, a(n) for n = 1..10000</a> %o A171865 (Haskell) %o A171865 import Data.List (elemIndices) %o A171865 a171865 n = a171865_list !! (n-1) %o A171865 a171865_list = map (+ 1) $ elemIndices 0 a181391_list %o A171865 -- _Reinhard Zumkeller_, Oct 31 2011 %o A171865 (Python) %o A171865 A181391_list, A171865_list = [0, 0], [1,2] %o A171865 for n in range(1, 10**4): %o A171865 for m in range(n-1, -1, -1): %o A171865 if A181391_list[m] == A181391_list[n]: %o A171865 A181391_list.append(n-m) %o A171865 break %o A171865 else: %o A171865 A181391_list.append(0) %o A171865 A171865_list.append(n+2) # _Chai Wah Wu_, Jan 02 2015 %Y A171865 Cf. A181391, A171868. %K A171865 nonn %O A171865 1,2 %A A171865 _N. J. A. Sloane_, Oct 17 2010