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 A189641 #11 Apr 24 2021 03:27:46 %S A189641 0,0,1,1,1,2,3,3,4,4,4,5,5,5,6,7,7,8,9,9,10,10,10,11,12,12,13,13,13, %T A189641 14,14,14,15,16,16,17,17,17,18,18,18,19,20,20,21,22,22,23,23,23,24,25, %U A189641 25,26,27,27,28,28,28,29,30,30,31,31,31,32,32,32,33,34,34,35,36,36,37,37,37,38,39,39,40 %N A189641 Partial sums of A189640. %C A189641 See A189640. %F A189641 a(n) = a(floor((n+2)/3)) + floor(n/3), where a(1)=0. %t A189641 (See A189640.) %o A189641 (PARI) a(n) = n--; (n - vecsum(digits(n,3)%2))/2; \\ _Kevin Ryde_, Apr 23 2021 %Y A189641 Cf. A189640, A189672 (essentially the same). %K A189641 nonn %O A189641 1,6 %A A189641 _Clark Kimberling_, Apr 24 2011