Checking if the whole number is prime, and if all its digits are too
The easiest improvement to make is to only go up to n**.5 inisprime This yields a quadratic speedup. The next obvious improvement is to not convert each digit to an int, but rather just use if j not in "2357":. This saves time in two ways: First, it skips an int conversion, and secondly, it uses one check instead of a for loop.