665611621 has 4 divisors (see below), whose sum is σ = 666765772. Its totient is φ = 664457472.

The previous prime is 665611619. The next prime is 665611631. The reversal of 665611621 is 126116566.

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 373030596 + 292581025 = 19314^2 + 17105^2 .

It is a cyclic number.

It is not a de Polignac number, because 665611621 - 2¹ = 665611619 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 (665611601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 576210 + ... + 577363.

It is an arithmetic number, because the mean of its divisors is an integer number (166691443).

Almost surely, 2^665611621 is an apocalyptic number.

It is an amenable number.

665611621 is a deficient number, since it is larger than the sum of its proper divisors (1154151).

665611621 is a wasteful number, since it uses less digits than its factorization.

665611621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1154150.

The product of its digits is 12960, while the sum is 34.

The square root of 665611621 is about 25799.4500135177. The cubic root of 665611621 is about 873.1193877802.

The spelling of 665611621 in words is "six hundred sixty-five million, six hundred eleven thousand, six hundred twenty-one".