721787561 has 16 divisors (see below), whose sum is σ = 834164160. Its totient is φ = 617647680.

The previous prime is 721787519. The next prime is 721787579. The reversal of 721787561 is 165787127.

It is a cyclic number.

It is not a de Polignac number, because 721787561 - 2⁶ = 721787497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (721787501) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 21815 + ... + 43811.

It is an arithmetic number, because the mean of its divisors is an integer number (52135260).

Almost surely, 2^721787561 is an apocalyptic number.

It is an amenable number.

721787561 is a deficient number, since it is larger than the sum of its proper divisors (112376599).

721787561 is a wasteful number, since it uses less digits than its factorization.

721787561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22184.

The product of its digits is 164640, while the sum is 44.

The square root of 721787561 is about 26866.1043138003. The cubic root of 721787561 is about 897.0220756038.

The spelling of 721787561 in words is "seven hundred twenty-one million, seven hundred eighty-seven thousand, five hundred sixty-one".