%I #18 Jun 06 2023 03:52:51
%S 9,11,12,13,14,15,16,17,18,19,21,22,23,24,25,26,27,28,29,31,32,33,34,
%T 35,36,37,38,39,41,42,43,44,45,46,47,48,49,51,52,53,54,55,56,57,58,59,
%U 61,62,63,64,65,66,67,68,69,71,72,73,74,75,76,77,78,79,81,82,90,92,93,94,95,96,97,98,100,101,109,111
%N Numbers with exactly two distinct base-9 digits.
%p isA031954 := proc(n)
%p local dgs,p,s ;
%p dgs := convert(convert(n,base,9),set) ;
%p if nops(dgs) = 2 then
%p true ;
%p else
%p false ;
%p end if ;
%p end proc:
%p A031954 := proc(n)
%p option remember ;
%p if n =1 then
%p 9 ;
%p else
%p for a from procname(n-1)+1 do
%p if isA031954(a) then
%p return a;
%p end if;
%p end do:
%p end if;
%p end proc:
%p seq(A031954(n),n=1..80) ; # _R. J. Mathar_, Jan 24 2023
%o (PARI) a(n)=n+8+(n+7)\9 \\ _Charles R Greathouse IV_, Mar 10 2021
%Y Cf. A007095.
%K nonn,base,easy
%O 1,1
%A _Clark Kimberling_