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

A089690

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