721647 has 12 divisors (see below), whose sum is σ = 1050504. Its totient is φ = 477360.

The previous prime is 721631. The next prime is 721661. The reversal of 721647 is 746127.

It is not a de Polignac number, because 721647 - 2⁴ = 721631 is a prime.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 721647.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1408 + ... + 1850.

It is an arithmetic number, because the mean of its divisors is an integer number (87542).

2⁷²¹⁶⁴⁷ is an apocalyptic number.

721647 is a deficient number, since it is larger than the sum of its proper divisors (328857).

721647 is a wasteful number, since it uses less digits than its factorization.

721647 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 630 (or 627 counting only the distinct ones).

The product of its digits is 2352, while the sum is 27.

The square root of 721647 is about 849.4980871079. The cubic root of 721647 is about 89.6963843093.

The spelling of 721647 in words is "seven hundred twenty-one thousand, six hundred forty-seven".