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 A217556 #11 Dec 23 2024 14:53:43
%S A217556 1,2,3,4,5,6,7,8,9,20,11,22,13,24,15,26,17,28,19,40,31,42,33,44,35,46,
%T A217556 37,48,39,60,51,62,53,64,55,66,57,68,59,80,71,82,73,84,75,86,77,88,79,
%U A217556 200,91,202,93,204,95,206,97,208,99,210,101,212,103,214,105,216,107,218,109
%N A217556 Terms as well as ending/starting digits are of alternating parity; this is the lexicographically earliest injective sequence with this property.
%H A217556 E. Angelini, <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2012-October/010252.html">Odd/even: integers and digits alternate</a>, SeqFan mailing list, Oct 06 2012
%o A217556 (PARI) A217556(n,show=0,a=1,u)={for( i=2, n, u+=1<<a; show & print1(a","); for(t=1,9e9, bittest(u,t) & next; bittest(t+a,0) || next; !bittest(a%10 + t\10^(#Str(t)-1),0) & (t+=10^(#Str(t)-1)-1) & next; a=t; break )); a} \\ - _M. F. Hasler_, Oct 06 2012
%Y A217556 A simplified variant of A217555.
%Y A217556 See also A217559, A217560, where "parity" is replaced by "primality".
%K A217556 nonn,base
%O A217556 1,2
%A A217556 _Eric Angelini_ and _M. F. Hasler_, Oct 06 2012