861644721 has 16 divisors (see below), whose sum is σ = 1355337728. Its totient is φ = 476485200.

The previous prime is 861644701. The next prime is 861644741. The reversal of 861644721 is 127446168.

It is an interprime number because it is at equal distance from previous prime (861644701) and next prime (861644741).

It is not a de Polignac number, because 861644721 - 2⁶ = 861644657 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 861644721.

It is not an unprimeable number, because it can be changed into a prime (861644701) 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, 661135 + ... + 662436.

It is an arithmetic number, because the mean of its divisors is an integer number (84708608).

Almost surely, 2^861644721 is an apocalyptic number.

It is an amenable number.

861644721 is a deficient number, since it is larger than the sum of its proper divisors (493693007).

861644721 is a wasteful number, since it uses less digits than its factorization.

861644721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1323612.

The product of its digits is 64512, while the sum is 39.

The square root of 861644721 is about 29353.7854628666. The cubic root of 861644721 is about 951.5743870059.

The spelling of 861644721 in words is "eight hundred sixty-one million, six hundred forty-four thousand, seven hundred twenty-one".