821105721 has 16 divisors (see below), whose sum is σ = 1217049600. Its totient is φ = 547135344.

The previous prime is 821105717. The next prime is 821105737. The reversal of 821105721 is 127501128.

821105721 is a `hidden beast` number, since 82 + 1 + 10 + 572 + 1 = 666.

It is not a de Polignac number, because 821105721 - 2² = 821105717 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (821105741) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 59560 + ... + 72038.

It is an arithmetic number, because the mean of its divisors is an integer number (76065600).

Almost surely, 2^821105721 is an apocalyptic number.

It is an amenable number.

821105721 is a deficient number, since it is larger than the sum of its proper divisors (395943879).

821105721 is a wasteful number, since it uses less digits than its factorization.

821105721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14925 (or 14919 counting only the distinct ones).

The product of its (nonzero) digits is 1120, while the sum is 27.

The square root of 821105721 is about 28654.9423485723. The cubic root of 821105721 is about 936.4106822896.

Adding to 821105721 its reverse (127501128), we get a palindrome (948606849).

The spelling of 821105721 in words is "eight hundred twenty-one million, one hundred five thousand, seven hundred twenty-one".