RosettaCodeData/Task/Digital-root-Multiplicative-digital-root/J/digital-root-multiplicative-digital-root-4.j

   (<:@#,{:) */@(10&#.inv)^:a: 123321
3 8
   (<:@#,{:) */@(10&#.inv)^:a: 7739
3 8
   (<:@#,{:) */@(10&#.inv)^:a: 893
3 2
   (<:@#,{:) */@(10&#.inv)^:a: 899998
2 0