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 A130048 #3 Mar 30 2012 18:57:10 %S A130048 1,2,4,5,8,9,10,11,13,14,15,16,18,19,21,22,23,24,25,26,27,28,30,31,33, %T A130048 34,35,36,37,38,40,41,42,43,44,45,46,47,48,49,52,53,54,55,56,57,58,59, %U A130048 60,61,62,64,65,66,67,68,69,70,71,73,74,75,76,78,79,80,81,82,83,84,85 %N A130048 Complement of inductive sum sequence A130049. %F A130048 a(1)=1, a(2)=2, b(1)=0, b(2)=3; for n>=3, let x=Floor(n/2) and y=n-x+1. Then a(n)=least positive integer not among a(1),a(2),...,a(n-1), b(1),b(2),...b(n-1) and b(n)=a(1)+a(2)+...+a(x) if n is even, b(n)=a(y)+a(y+1)+...+a(n) if n is odd. %e A130048 (a(1),a(2),...,a(6))=(1,2,4,5,8,9), so x=4 and b(6)=1+2+4+5=12. %e A130048 (a(1),a(2),...,a(7))=(1,2,4,5,8,9,10), so y=4 and b(7)=5+8+9+10=32. %Y A130048 Cf. A130049, A130050, A130051. %K A130048 nonn %O A130048 1,2 %A A130048 _Clark Kimberling_, May 03 2007