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 A228586 #10 Feb 06 2015 10:06:42
%S A228586 4,6,9,0,1,4,1,5,1,1,2,2,2,5,2,6,2,3,3,4,3,5,3,8,3,9,3,6,4,9,4,1,5,5,
%T A228586 5,7,5,8,5,2,6,5,6,9,6,4,7,7,7,2,8,5,8,6,8,7,8,1,9,3,9,4,9,5,9,6,0,1,
%U A228586 1,1,1,5,1,1,8,1,1,9,1,1,1,2,1
%N A228586 Write the semiprimes backwards in base 10 and juxtapose (concatenate) their digits.
%C A228586 Also, decimal expansion of the constant 0.46901415112225262... This is to A228355 as semiprimes A001358 are to prime A000040.
%C A228586 A theorem of Copeland & Erdős proves that this constant is 10-normal. - _Charles R Greathouse IV_, Feb 06 2015
%H A228586 A. H. Copeland and P. Erdős, <a href="http://www.renyi.hu/~p_erdos/1946-01.pdf">Note on normal numbers</a>, Bull. Amer. Math. Soc. 52 (1946), pp. 857-860.
%e A228586 4, 6, 9, 01, 41, 51, 12, 22, 52, 62, 33, 43, 53, 83, 93, 64, 94, 15, 55,...
%o A228586 (PARI) print1(4); for(n=6, 121, if(bigomega(n)==2, d=Vecrev(digits(n)); for(i=1, #d, print1(", "d[i])))) \\ _Charles R Greathouse IV_, Feb 06 2015
%Y A228586 Cf. A001358, A228355.
%K A228586 nonn,base,easy,cons
%O A228586 1,1
%A A228586 _Jonathan Vos Post_, Aug 26 2013