721649 has 4 divisors (see below), whose sum is σ = 744960. Its totient is φ = 698340.

The previous prime is 721631. The next prime is 721661. The reversal of 721649 is 946127.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 721649 - 2¹⁶ = 656113 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 721649.

It is not an unprimeable number, because it can be changed into a prime (721619) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11609 + ... + 11670.

It is an arithmetic number, because the mean of its divisors is an integer number (186240).

2⁷²¹⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

721649 is a deficient number, since it is larger than the sum of its proper divisors (23311).

721649 is a wasteful number, since it uses less digits than its factorization.

721649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23310.

The product of its digits is 3024, while the sum is 29.

The square root of 721649 is about 849.4992642728. The cubic root of 721649 is about 89.6964671719.

The spelling of 721649 in words is "seven hundred twenty-one thousand, six hundred forty-nine".