%N a(1)=4, then a(n) is the smallest semiprime not occurring earlier, not ending with zero and starting with the last digit of a(n-1).
%H David A. Corneth, <a href="/A119729/b119729.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Zak Seidov)
%Y Cf. A000030, A001358, A010879.
%A _Jonathan Vos Post_, Jun 14 2006