%I #22 Mar 08 2022 08:25:13
%S 1,11,12,21,101,102,201,1001,1002,2001,10001,10002,20001,100001,
%T 100002,200001,1000001,1000002,2000001,10000001,10000002,20000001,
%U 100000001,100000002,200000001,1000000001,1000000002,2000000001,10000000001
%N a(1) = 1 and a(n+1) is the least number > a(n) that begins with the last digit of a(n) and doesn't end with 0.
%C a(n) must be chosen with nonzero rightmost digit.
%F For n == 0 (mod 3), a(n) = 10^(n/3) + 2; for n == 1 (mod 3), n>1, a(n) = 2*10^((n-1)/3) + 1; for n == 2 (mod 3), a(n) = 10^((n+1)/3) + 1. - _Sam Alexander_, Jan 04 2005
%F From _Chai Wah Wu_, Jun 02 2016: (Start)
%F a(n) = 11*a(n-3) - 10*a(n-6) for n > 7.
%F G.f.: x*(1 + x + 2*x^2)*(1 + 10*x - 10*x^3 - 10*x^4)/((1 - x)*(1 - 10*x^3)*(1 + x + x^2)). (End)
%F a(n) = (1-sign((n-1) mod 3))*10^floor(n/3)+10^floor((n+1)/3)-sign(n mod 3)+2, for n > 1. - _Wesley Ivan Hurt_, Mar 06 2022
%Y Cf. A076654.
%Y Cf. A101233.
%K base,easy,nonn
%O 1,2
%A _Eric Angelini_, Oct 01 2004
%E More terms from _Sam Alexander_, Jan 04 2005
%E More terms from _David Wasserman_, Feb 26 2008