721606 has 4 divisors (see below), whose sum is σ = 1082412. Its totient is φ = 360802.

The previous prime is 721597. The next prime is 721613. The reversal of 721606 is 606127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 606127 = 71 ⋅8537.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an Ulam number.

It is a congruent number.

It is an unprimeable number.

721606 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 180400 + ... + 180403.

It is an arithmetic number, because the mean of its divisors is an integer number (270603).

2⁷²¹⁶⁰⁶ is an apocalyptic number.

721606 is a deficient number, since it is larger than the sum of its proper divisors (360806).

721606 is a wasteful number, since it uses less digits than its factorization.

721606 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 360805.

The product of its (nonzero) digits is 504, while the sum is 22.

The square root of 721606 is about 849.4739548685. The cubic root of 721606 is about 89.6946855926.

The spelling of 721606 in words is "seven hundred twenty-one thousand, six hundred six".