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 A120444 #19 Dec 09 2024 11:00:52
%S A120444 0,1,0,3,-1,5,0,4,1,9,-5,11,3,5,0,15,-4,17,-3,9,7,21,-13,18,9,13,-1,
%T A120444 27,-13,29,0,17,13,21,-20,35,15,21,-11,39,-13,41,3,11,19,45,-29,40,6,
%U A120444 29,5,51,-13,37,-9,33,25,57,-49,59,27,21,0,45,-13,65,9,41,-5,69,-52,71,33,25,11,57,-13,77,-27,40,37,81,-57,61,39,53,-5
%N A120444 First differences of A004125.
%C A120444 It appears that (1) a(n)=0 if and only if n is a power of 2 and (2) a(n)=n-1 if and only if n+1 is a prime. (This has been verified for the first 2000 terms.)
%H A120444 Reinhard Zumkeller, <a href="/A120444/b120444.txt">Table of n, a(n) for n = 1..10000</a>
%F A120444 a(n) = A005408(n) - A000203(n+1). - _Omar E. Pol_, Jan 24 2014
%t A120444 Table[2*m - 1 - DivisorSigma[1, m], {m, 2, 100}] (* _Paolo Xausa_, Dec 09 2024 *)
%o A120444 (Haskell)
%o A120444 a120444 n = a120444_list !! (n-1)
%o A120444 a120444_list = zipWith (-) (tail a004125_list) a004125_list
%o A120444 -- _Reinhard Zumkeller_, May 30 2015
%Y A120444 Cf. A000203, A004125, A005408.
%K A120444 sign,easy
%O A120444 1,4
%A A120444 _John W. Layman_, Jul 19 2006