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 A221476 #3 Feb 14 2013 20:59:07
%S A221476 2,5,113,227,2417,3637,7253,14549,14563,30559,38677,38833,155333,
%T A221476 206923,207121,217309,464213,466033,620771,827693,915737,1100149,
%U A221476 1100353,1220983,1303873,1472893,1656901,1963813,2327483,2475797,2933717,2933731,3313777,3491083
%N A221476 Prime numbers having no additional odd primes in their Collatz (3x+1) trajectory.
%C A221476 Sequence A221475 contains odd composite numbers with this property.
%H A221476 <a href="/index/3#3x1">Index entries for sequences related to 3x+1 (or Collatz) problem</a>
%t A221476 Collatz[n_] := NestWhileList[If[EvenQ[#], #/2, 3 # + 1] &, n, # > 1 &]; t = {}; n = 0; While[Length[t] < 50, n++; p = Prime[n]; If[Union[Drop[PrimeQ[Rest[Collatz[p]]], -2]] == {False}, AppendTo[t, p]]]; t
%Y A221476 Cf. A221475.
%K A221476 nonn
%O A221476 1,1
%A A221476 _T. D. Noe_, Feb 14 2013