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 A171950 #21 Sep 08 2022 08:45:50
%S A171950 1,1,1,0,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,
%T A171950 25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,
%U A171950 48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68
%N A171950 a(1)=1. a(n) = the absolute difference between (the sum of previous terms) and A000217(n-2), n>1.
%H A171950 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).
%F A171950 a(n) = |Sum_{i=1..n-1} a(i) - A000217(n-2)|, n>1.
%F A171950 a(n) = n-2, n>=5. - _R. J. Mathar_, Oct 26 2010
%t A171950 LinearRecurrence[{2,-1},{1,1,1,0,3,4},70] (* _Harvey P. Dale_, Dec 10 2015;; a(1)=1 amended by _Georg Fischer_, Apr 03 2019 *)
%o A171950 (PARI) a(n)=if(n>4,n-2,n<4) \\ _Charles R Greathouse IV_, Oct 27 2011
%o A171950 (Magma) [1,1,1,0] cat [n-2: n in [5..70]]; // _G. C. Greubel_, Apr 03 2019
%o A171950 (Sage) [1,1,1,0]+[n-2 for n in (5..70)] # _G. C. Greubel_, Apr 03 2019
%Y A171950 Cf. A000217, A065475.
%K A171950 easy,nonn,less
%O A171950 1,5
%A A171950 _Giovanni Teofilatto_, Oct 20 2010
%E A171950 Zero inserted, precise indices added in definition, keyword:less and two formulas added - _R. J. Mathar_, Oct 26 2010
%E A171950 A171950 and A181440 are two different edited versions of a sequence submitted by Giovanni Teofilatto. - _N. J. A. Sloane_, Oct 29 2010