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 A006508 M3357 #42 May 02 2018 14:42:10
%S A006508 1,4,9,16,26,39,56,78,106,141,184,236,299,374,465,570,696,843,1014,
%T A006508 1212,1441,1708,2014,2365,2769,3226,3749,4343,5016,5774,6630,7596,
%U A006508 8676,9897,11259,12784,14482,16383,18502,20847,23458,26354,29562,33112,37041,41370
%N A006508 a(n+1) = a(n)-th composite number, with a(0) = 1.
%C A006508 Generated by a sieve: start with natural numbers, remove those terms which occupy positions which are prime, leaving 1,4,6,8,9,10,12,14,15,16,18,...; remove those terms whose positions are primes plus one; leaving 1,4,9,12,15,16,18,...; remove those whose positions are primes plus two; continue. - _Robert G. Wilson v_, Jan 06 2008
%C A006508 Number of terms <= 10^k, k=0..: 1, 3, 8, 18, 34, 54, 80, 110, 147, 188, 235, 287, 345, 407, 475, ..., . - _Robert G. Wilson v_, Jan 06 2008
%C A006508 The first occurrence of a k-almost prime or 0 if not present: 1, 0, 4, 78, 16, 696, 5016, 95920, 46144, 10236034900, 600374208, 1613472, 21565696412400, 0, 24323590656, ..., . - _Robert G. Wilson v_, Jan 06 2008
%D A006508 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006508 Chai Wah Wu, <a href="/A006508/b006508.txt">Table of n, a(n) for n = 0..900</a> (n = 0..503 from Robert G. Wilson v)
%H A006508 Popular Computing (Calabasas, CA), <a href="/A006508/a006508.png">Contest 5 Results</a>. Annotated and scanned copy of page PC41-15 of Vol. 4 (No. 41, Aug 1976).
%H A006508 <a href="/index/Si#sieve">Index entries for sequences generated by sieves</a>
%t A006508 Composite[n_Integer] := FixedPoint[n + PrimePi@# + 1 &, n + PrimePi@n + 1]; NestList[ Composite@# &, 1, 45] (* _Labos Elemer_ *)
%t A006508 With[{c=Select[Range[42000],CompositeQ]},NestList[c[[#]]&,1,45]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Mar 03 2018 *)
%o A006508 (Haskell)
%o A006508 a006508 n = a006508_list !! n
%o A006508 a006508_list = iterate a002808 1 -- _Reinhard Zumkeller_, Oct 24 2011
%Y A006508 Cf. A007097, A002808.
%K A006508 nonn,easy
%O A006508 0,2
%A A006508 _N. J. A. Sloane_
%E A006508 Edited by _Robert G. Wilson v_, Jan 06 2008