665366821 has 8 divisors (see below), whose sum is σ = 778103744. Its totient is φ = 557051040.

The previous prime is 665366813. The next prime is 665366837. The reversal of 665366821 is 128663566.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 665366821 - 2³ = 665366813 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (43).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665366851) 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, 1104960 + ... + 1105561.

It is an arithmetic number, because the mean of its divisors is an integer number (97262968).

Almost surely, 2^665366821 is an apocalyptic number.

It is an amenable number.

665366821 is a deficient number, since it is larger than the sum of its proper divisors (112736923).

665366821 is a wasteful number, since it uses less digits than its factorization.

665366821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2210571.

The product of its digits is 311040, while the sum is 43.

The square root of 665366821 is about 25794.7052900397. The cubic root of 665366821 is about 873.0123354452.

The spelling of 665366821 in words is "six hundred sixty-five million, three hundred sixty-six thousand, eight hundred twenty-one".