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 A216289 #5 Sep 03 2012 22:34:27
%S A216289 20,9,2,4,0
%N A216289 Smallest k in which there are exactly n primes between 10*k and 10*k+9.
%t A216289 mx = 5; t = Table[-1, {mx}]; n = 0; found = 0; While[found < mx, ps = Select[Range[10*n, 10*n + 9], PrimeQ]; len = Length[ps]; If[t[[len + 1]] == -1, t[[len + 1]] = n; found++]; n++]; t (* _T. D. Noe_, Sep 03 2012 *)
%Y A216289 Cf. A186311, A032352, A007811, A078494.
%K A216289 nonn,fini,full
%O A216289 0,1
%A A216289 _V. Raman_, Sep 03 2012