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 A133225 #13 Sep 16 2015 14:02:43
%S A133225 2,2,3,5,7,11,13,19,31,43,61,89,127,181,251,359,509,719,1021,1447,
%T A133225 2039,2887,4093,5791,8191,11579,16381,23167,32749,46337,65521,92681,
%U A133225 131071,185363,262139,370723,524287,741431,1048573,1482907,2097143,2965819
%N A133225 Largest prime <= 2^((n+1)/2).
%C A133225 If one is trying to decide whether an n+1 digit binary number is prime, this is the largest prime for which one needs to test divisibility. For example a six digit number like 110101 must be below 64, so only primes up to 7 are needed to test divisibility. Compare with sequence A132153.
%H A133225 Harvey P. Dale, <a href="/A133225/b133225.txt">Table of n, a(n) for n = 1..1000</a>
%F A133225 a(n) = A007917[A017910(n+1)]. - _R. J. Mathar_
%p A133225 seq(prevprime(floor(2^((n+1)*1/2))+1),n=1..40); # _Emeric Deutsch_
%p A133225 A017910 := proc(n) floor(2^(n/2)) ; end: A007917 := proc(n) prevprime(n+1) ; end: A133225 := proc(n) A007917(A017910(n+1)) ; end: seq(A133225(n),n=1..60) ; # _R. J. Mathar_
%t A133225 PrevPrim[n_] := Block[{k = n}, While[ !PrimeQ@k, k-- ]; k]; f[n_] := PrevPrim@ Floor@ Sqrt[2^(n + 1)]; Array[f, 42] (* _Robert G. Wilson v_ *)
%t A133225 Table[Prime[PrimePi[2^((n + 1)/2)]], {n, 1, 50}] (* _Stefan Steinerberger_ *)
%t A133225 lp[n_]:=Module[{c=2^((n+1)/2)},If[PrimeQ[c],c,NextPrime[c,-1]]]; Array[lp,50] (* _Harvey P. Dale_, Aug 25 2013 *)
%Y A133225 Cf. A132153.
%K A133225 nonn
%O A133225 1,1
%A A133225 _Anthony C Robin_, Jan 03 2008
%E A133225 More terms from _Stefan Steinerberger_, _R. J. Mathar_, _Robert G. Wilson v_ and _Emeric Deutsch_, Jan 06 2008