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a(n) is the smallest positive number not yet in the sequence that contains exactly one even digit and exactly one odd digit from a(n-1), and no digit in a(n) is repeated.
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%I #34 Jan 12 2025 09:06:32

%S 10,102,12,21,120,103,30,130,104,14,41,124,123,23,32,132,125,25,52,

%T 152,126,16,61,106,105,50,150,107,70,170,108,18,81,128,127,27,72,172,

%U 129,29,92,192,142,134,34,43,143,140,109,90,190,160,136,36,63,163

%N a(n) is the smallest positive number not yet in the sequence that contains exactly one even digit and exactly one odd digit from a(n-1), and no digit in a(n) is repeated.

%H Robert Israel, <a href="/A309540/b309540.txt">Table of n, a(n) for n = 1..40534</a>

%e a(2)=102: a(2) is not 100 (since zero would be repeated), nor 101 (since 1 would be repeated).

%p filter:= proc(n) local L;

%p L:= convert(n,base,10);

%p nops(L) = nops(convert(L,set)) and convert(L mod 2,set) = {0,1};

%p end proc:

%p Cands:= select(filter, [$11 .. 1000]): nC:= nops(Cands):

%p R:= 10: r:= 10: r0, r1:= selectremove(type, convert(convert(r,base,10),set),even):

%p for count from 1 do

%p found:= false;

%p for i from 1 to nC+1-count do

%p x:= Cands[i];

%p Lx:= convert(convert(x,base,10),set);

%p if nops(Lx intersect r0) = 1 and nops(Lx intersect r1) = 1 then

%p found:= true;

%p R:= R, x;

%p r:= x;

%p Cands:= subsop(i=NULL, Cands);

%p r0, r1:= selectremove(type, convert(convert(r,base,10),set),even);

%p break

%p fi

%p od;

%p if not found then break fi;

%p od:

%p R; # _Robert Israel_, Jan 09 2025

%Y Cf. A184992, A318700, A309390, A309539, A076654.

%K nonn,base,fini,full,look

%O 1,1

%A _Enrique Navarrete_, Aug 06 2019

%E Edited by _Robert Israel_, Jan 10 2025