a={1,3,7,9} a1={1,3,7,9,0} b[n]=Flatten[Table[10*Sum[10^m*a1[[1+Mod[m,5]]],{m,0,n}]+a,{n,0,digits}]]; a(m) = if b[n] is prime then b[n].

A089691

a={1,3,7,9} a1={1,3,7,9,0} b[n]=Flatten[Table[10*Sum[10^m*a1[[1+Mod[m,5]]],{m,0,n}]+a,{n,0,digits}]]; a(m) = if b[n] is prime then b[n].