Enter the largest four-digit octal number whose binary notation contains 4 ones.

One digit of an octal number contains digits from “0” to “7”, resulting in a total of eight digits. Thus, one digit of an octal number is encoded by three digits of a binary number: 7 (8) = 111 (2), where (8) is the prefix of the octal number, (2) is the prefix of the binary number. According to the condition, it is said that the octal number must be four-digit (four-digit), and one octal digit requires 3 binary digits, which means: 4 * 3 = 12 (bits) To write a four-digit octal number, twelve binary digits are needed. And since a binary number contains 4 units and the number must be as large as possible, then these units should be located on the left: 1111’0000’0000 (2) = 7400 (8).