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 A100351 #5 Mar 30 2012 18:39:35
%S A100351 8,4311
%N A100351 Numbers n such that n-2^k is a semiprime for all k > 0 with 2^k < n.
%C A100351 A subset of A100349. No others < 10^9; conjecture that this sequence is finite.
%C A100351 Next term, if it exists, exceeds 5*10^10. [From _Sean A. Irvine_, Apr 13 2010]
%e A100351 4311-2=31*139, 4311-4=59*73, 4311-8=13*331, 4311-16=5*859, 4311-32=11*389, 4311-64=31*137, 4311-128=47*89, 4311-256=5*811, 4311-512=29*131, 4311-1024=19*173, 4311-2048=31*73, 4311-4096=5*43
%t A100351 SemiPrimeQ[n_Integer] := If[Abs[n]<2, False, (2==Plus@@Transpose[FactorInteger[Abs[n]]][[2]])]; lst={}; Do[k=1; While[p=n-2^k; p>0 && SemiPrimeQ[p], k++ ]; If[p<=0, AppendTo[lst, n]], {n, 3, 1000000}]; lst
%Y A100351 Cf. A039669 (n such that n-2^k is prime), A100349 (n such that n-2^k is prime or semiprime), A100350 (primes p such that p-2^k is prime or semiprime).
%K A100351 bref,more,nonn
%O A100351 1,1
%A A100351 _T. D. Noe_, Nov 18 2004