721661605 has 8 divisors (see below), whose sum is σ = 989707392. Its totient is φ = 494853648.

The previous prime is 721661597. The next prime is 721661663. The reversal of 721661605 is 506166127.

It is a happy number.

721661605 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 721661605 - 2³ = 721661597 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10309417 + ... + 10309486.

It is an arithmetic number, because the mean of its divisors is an integer number (123713424).

Almost surely, 2^721661605 is an apocalyptic number.

It is an amenable number.

721661605 is a deficient number, since it is larger than the sum of its proper divisors (268045787).

721661605 is a wasteful number, since it uses less digits than its factorization.

721661605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20618915.

The product of its (nonzero) digits is 15120, while the sum is 34.

The square root of 721661605 is about 26863.7600681662. The cubic root of 721661605 is about 896.9698940980.

The spelling of 721661605 in words is "seven hundred twenty-one million, six hundred sixty-one thousand, six hundred five".