665525221 has 4 divisors (see below), whose sum is σ = 665606700. Its totient is φ = 665443744.

The previous prime is 665525213. The next prime is 665525239. The reversal of 665525221 is 122525566.

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 154132225 + 511392996 = 12415^2 + 22614^2 .

It is a cyclic number.

It is not a de Polignac number, because 665525221 - 2³ = 665525213 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 (665525261) 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, 26926 + ... + 45343.

It is an arithmetic number, because the mean of its divisors is an integer number (166401675).

Almost surely, 2^665525221 is an apocalyptic number.

It is an amenable number.

665525221 is a deficient number, since it is larger than the sum of its proper divisors (81479).

665525221 is an equidigital number, since it uses as much as digits as its factorization.

665525221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81478.

The product of its digits is 36000, while the sum is 34.

The square root of 665525221 is about 25797.7755048764. The cubic root of 665525221 is about 873.0816076007.

The spelling of 665525221 in words is "six hundred sixty-five million, five hundred twenty-five thousand, two hundred twenty-one".