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A217556 Terms as well as ending/starting digits are of alternating parity; this is the lexicographically earliest injective sequence with this property. 4

%I

%S 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 37,48,39,60,51,62,53,64,55,66,57,68,59,80,71,82,73,84,75,86,77,88,79,

%U 200,91,202,93,204,95,206,97,208,99,210,101,212,103,214,105,216,107,218,109

%N Terms as well as ending/starting digits are of alternating parity; this is the lexicographically earliest injective sequence with this property.

%H E. Angelini, <a href="http://list.seqfan.eu/pipermail/seqfan/2012-October/010252.html">Odd/even: integers and digits alternate</a>, SeqFan mailing list, Oct 06 2012

%o (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 A simplified variant of A217555.

%Y See also A217559, A217560, where "parity" is replaced by "primality".

%K nonn,base

%O 1,2

%A _Eric Angelini_ and _M. F. Hasler_, Oct 06 2012

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Last modified February 27 04:56 EST 2020. Contains 332299 sequences. (Running on oeis4.)