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 A161975 #8 Mar 07 2019 23:27:48
%S A161975 4,11,21,30,34,57,69,92,108,143,174,186,175,264,280,246,342,351,420,
%T A161975 483,470,424,564,621,531,660,765,837,885,980,781,1121,1134,1209,1136,
%U A161975 1242,1430,1420,1518,1422,1246,1764,1425,1938,2014,1992,2091,2136,2090,2394
%N A161975 Sum_{x=sum of prime factors of n-th composite..n-th composite} x.
%e A161975 4(=4), 11(=(2+3)+6), 22(=(2+2+2)+7+8), 30(=(3+3)+7+9), 34(=(2+5)+8+9+10), etc.
%p A161975 A002808 := proc(n) option remember ; if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: A001414 := proc(n) pfs :=ifactors(n)[2] ; add(op(1,p)*op(2,p) ,p=pfs) ; end: A046343 := proc(n) A001414(A002808(n)); end: A000217 := proc(n) n*(n+1)/2 ; end: A161975 := proc(n) A000217( A002808(n)) - A000217(A046343(n)-1) ; end: seq(A161975(n),n=1..90) ; # _R. J. Mathar_, Aug 03 2009
%o A161975 (PARI) a(n)=my(c=n+n\log(n+1),f);for(i=0,n-c+primepi(c),if(isprime(c++),i--));f=factor(c);binomial(c+1,2)-binomial(sum(i=1,#f[,1],f[i,1]*f[i,2]),2)
%Y A161975 Cf. A002808.
%K A161975 nonn
%O A161975 1,1
%A A161975 _Juri-Stepan Gerasimov_, Jun 23 2009
%E A161975 a(3), a(12) and others corrected by _R. J. Mathar_, Aug 03 2009
%E A161975 Program by _Charles R Greathouse IV_, Oct 12 2009