821392661 has 4 divisors (see below), whose sum is σ = 825930924. Its totient is φ = 816854400.

The previous prime is 821392619. The next prime is 821392699. The reversal of 821392661 is 166293128.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 373223761 + 448168900 = 19319^2 + 21170^2 .

It is a cyclic number.

It is not a de Polignac number, because 821392661 - 2²⁶ = 754283797 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821392361) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2268860 + ... + 2269221.

It is an arithmetic number, because the mean of its divisors is an integer number (206482731).

Almost surely, 2^821392661 is an apocalyptic number.

It is an amenable number.

821392661 is a deficient number, since it is larger than the sum of its proper divisors (4538263).

821392661 is a wasteful number, since it uses less digits than its factorization.

821392661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4538262.

The product of its digits is 31104, while the sum is 38.

The square root of 821392661 is about 28659.9487264021. The cubic root of 821392661 is about 936.5197475746.

The spelling of 821392661 in words is "eight hundred twenty-one million, three hundred ninety-two thousand, six hundred sixty-one".