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 A101225 #17 Mar 18 2015 16:38:14
%S A101225 1,4,12,46,194,977,5492,33666,220068,1513371,10833076,80104927,
%T A101225 608455060,4726881850,37431015268,301327263751,2460711566651,
%U A101225 20348625806080,170149286304116,1436870802519360,12241980697771924,105136072207222852,909475787902559408,7919305232077304848
%N A101225 Numbers formed by the third nesting of pi(10^n).
%H A101225 Jonathan Bayless, Dominic Klyve, and Tomás Oliveira e Silva, <a href="http://www.emis.de/journals/INTEGERS/papers/n43/n43.Abstract.html">New Bounds and Computations on Prime-Indexed Primes</a>, INTEGERS, Electronic J. of Combinatorial Number Theory, Vol. 13, Paper A43, 2013.
%F A101225 a(n) = pi(pi(pi(10^n))) where pi(x) is the number of primes <= x.
%e A101225 a(3) = pi(pi(pi(10^3))) = 12, the third entry in the table.
%t A101225 f[n_] := Nest[PrimePi, 10^n, 3]; Table[ f[n], {n, 13}] (* _Robert G. Wilson v_, Dec 20 2004 *)
%o A101225 (PARI) nestpi(n,m) = { local(x,y,z); for(x=1,n,z=10^x;for(y=1,m,z=primepi(z));print1(z",")) }
%Y A101225 Cf. A006880, A096359.
%K A101225 nonn
%O A101225 1,2
%A A101225 _Cino Hilliard_, Dec 15 2004
%E A101225 More terms from _Robert G. Wilson v_, Dec 20 2004
%E A101225 a(16)-a(24) from _Robert G. Wilson v_, Mar 11 2015