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 A141620 #12 Mar 17 2025 14:37:33 %S A141620 5,-3,10,-3,-5,17,-3,-5,-7,26,-3,-5,-7,-9,37,-3,-5,-7,-9,-11,50,-3,-5, %T A141620 -7,-9,-11,-13,65,-3,-5,-7,-9,-11,-13,-15,82,-3,-5,-7,-9,-11,-13,-15, %U A141620 -17,101,-3,-5,-7,-9,-11,-13,-15,-17,-19,122,-3,-5,-7,-9,-11,-13,-15,-17,-19,-21 %N A141620 First differences of A120070. %F A141620 a(n) = mix (from 2) n^2+1 (or A002522(n+2)), (ever from -3) successive -A005408. %F A141620 a(n) = ((A^2+3*A-2*n)*(-A^2+A+2*(n+4))-(B^2+3*B-2*(n-1))*(-B^2+B+2*(n+3)))/4, where A = floor((sqrt(8*n+9)-1)/2) and B = floor((sqrt(8*(n-1)+9)-1)/2) = floor((sqrt(8*n+1)-1)/2). - _Luce ETIENNE_, May 31 2017 %Y A141620 Cf. A120070. Essentially the same as A133128. %K A141620 sign %O A141620 0,1 %A A141620 _Paul Curtz_, Aug 23 2008