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 A228584 #29 Dec 23 2024 14:53:43 %S A228584 1,9,2,2,9,9,4,4,9,9,6,6,9,9,8,8,9,1,0,0,1,1,0,0,3,1,0,0,5,1,0,0,7,1, %T A228584 0,0,9,1,2,2,1,1,2,2,3,1,2,2,5,1,2,2,7,1,2,2,9,1,4,4,1,1,4,4,3,1,4,4, %U A228584 5,1,4,4,7,1,4,4,9,1,6,6,1,1,6,6,3,1,6,6,5,1,6,6,7,1,6,6,9,1,8,8,1,1,8,8,3 %N A228584 Start with decimal expansion of Champernowne constant (A033307) and repeatedly remove the first digit between two neighbors (after the decimal point) having the same parity. %C A228584 Parity of digits is 1, 1, 0, 0, ... = A133872. %H A228584 Alois P. Heinz, <a href="/A228584/b228584.txt">Table of n, a(n) for n = 0..10000</a> %H A228584 Eric Angelini et al., <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2013-August/011621.html">Champernowne sieved</a> and follow-up messages on the SeqFan list, Aug 26 2013 %e A228584 Start with A033307 (decimal expansion of Champernowne's constant): 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 0, 1, 1, 1, 2, 1, 3, 1, 4, 1, 5, 1, 6, 1, 7, 1, 8, 1, 9, 2, 0, 2, 1, 2, 2, 2, 3, 2, 4, 2, 5, 2, 6, 2, 7, 2, 8, 2, 9, 3, 0, 3, 1, 3, 2, 3, 3, 3, 4, 3, 5, 3, 6, 3, 7, 3, 8, 3, 9, 4, 0, 4, 1, 4, 2, 4, 3, 4, 4, 4, 5, 4, 6, 4, 7, 4, 8, 4, 9, 5, 0, 5, 1, 5, 2, 5, 3, 5, 4, 5, 5, 5, 6, 5,... %e A228584 Now erase a digit when it is placed between two digits having the same parity -- and do this repeatedly. %e A228584 Example: %e A228584 1,2,3,... erase 2 %e A228584 You get now: %e A228584 1,3,4,5,... erase 4 %e A228584 You get now: 1,3,5,... erase 3 %e A228584 You get now: 1,5,6,7,... erase 6 %e A228584 You get now: 1,5,7,... erase 5 etc. %e A228584 The surviving digits are this sequence: %e A228584 1,9,2,2,9,9,4,4,9,9,6,6,9,9,8,8,9,1,0,0,1,1,0,... %e A228584 and the original "untouched" positive integers, A228585: %e A228584 1, 29, 49, 69, 89, 219, 239, 259, 279, 419, 439, ... %e A228584 We obtain a new constant, %e A228584 0.1922994499669988910011003100510071... %Y A228584 Cf. A033307, A133872, A228585 (untouched numbers in the removal process). %K A228584 nonn,cons,base %O A228584 0,2 %A A228584 _Alois P. Heinz_, Aug 26 2013