Concatenation of even n and odd n-th nonprime.

Terms

a(0) =21a(1) =69a(2) =1015a(3) =1421a(4) =2839a(5) =3245a(6) =4055a(7) =4257a(8) =4663a(9) =4865a(10) =6081a(11) =6891a(12) =7093a(13) =7295a(14) =86115a(15) =88117a(16) =90119a(17) =92121a(18) =94123a(19) =96125a(20) =102133a(21) =104135a(22) =108141a(23) =110143a(24) =112145a(25) =114147a(26) =118153a(27) =120155