721721905 has 8 divisors (see below), whose sum is σ = 866212200. Its totient is φ = 577280256.

The previous prime is 721721863. The next prime is 721721909. The reversal of 721721905 is 509127127.

It can be written as a sum of positive squares in 4 ways, for example, as 37847104 + 683874801 = 6152^2 + 26151^2 .

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 721721905 - 2¹¹ = 721719857 is a prime.

It is not an unprimeable number, because it can be changed into a prime (721721909) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44431 + ... + 58459.

It is an arithmetic number, because the mean of its divisors is an integer number (108276525).

Almost surely, 2^721721905 is an apocalyptic number.

It is an amenable number.

721721905 is a deficient number, since it is larger than the sum of its proper divisors (144490295).

721721905 is a wasteful number, since it uses less digits than its factorization.

721721905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24323.

The product of its (nonzero) digits is 8820, while the sum is 34.

The square root of 721721905 is about 26864.8823745796. The cubic root of 721721905 is about 896.9948761570.

The spelling of 721721905 in words is "seven hundred twenty-one million, seven hundred twenty-one thousand, nine hundred five".