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 A073839 #19 Aug 27 2015 02:48:55
%S A073839 0,4,10,18,33,45,53,84,94,105,138,162,201,256,272,289,340,411,431,510,
%T A073839 532,555,624,672,747,825,853,937,1024,1084,1116,1243,1342,1377,1482,
%U A073839 1519,1557,1708,1825,1866,1989,2073,2202,2377,2423,2561,2702,2893,2943
%N A073839 Sum of the composite numbers between n and 2n (both inclusive).
%C A073839 a(n) is the sum of A075084(n) composite numbers (A002808). - _Michel Marcus_, Aug 26 2015
%e A073839 a(6) = 6+8+9+10+12 = 45.
%p A073839 for n from 1 to 150 do l := 0:for j from n to 2*n do if not isprime(j) then l := l+j:fi:od:a[n] := l:od:a[1] := 0:seq(a[j],j=1..150);
%t A073839 cs[x_] := Flatten[Position[Table[PrimeQ[j], {j, x, 2*x}], False]]+x-1; sucs[x_] := Apply[Plus, cs[x]]; Table[sucs[w], {w, 1, 128}]
%t A073839 Join[{0}, Table[Plus @@ Select[Range[n, 2 n], ! PrimeQ[#] &], {n, 2, 49}]] (* _Jayanta Basu_, Aug 12 2013 *)
%o A073839 (PARI) a(n) = my(s=0); forcomposite (c=n, 2*n, s+=c); s; \\ _Michel Marcus_, Aug 26 2015
%Y A073839 Cf. A002808, A073840, A075084.
%K A073839 nonn
%O A073839 1,2
%A A073839 _Amarnath Murthy_, Aug 13 2002
%E A073839 More terms from _Sascha Kurz_ and _Labos Elemer_, Aug 14 2002