#Pyth, 11 10 bytes
Pyth, 11 10 bytes
!es*V*jT7l Accepts input as a list of digits. Try it online here, or verify all test cases at once here.
!es*V*jT7lQQ Implicit: Q=eval(input()) Trailing QQ implied jT7 10 in base 7 - yields [1,3] * lQ Repeat the above len(input) times *V Q Vectorised multiply the above with the input s Take the sum e % 10 ! Logical not Edit: saved a byte by replacing ,1 3 with jT7