665016221 has 8 divisors (see below), whose sum is σ = 670496184. Its totient is φ = 659545600.

The previous prime is 665016179. The next prime is 665016239. The reversal of 665016221 is 122610566.

It can be written as a sum of positive squares in 4 ways, for example, as 107536900 + 557479321 = 10370^2 + 23611^2 .

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665016221 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 (665016721) 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, 236021 + ... + 238821.

It is an arithmetic number, because the mean of its divisors is an integer number (83812023).

Almost surely, 2^665016221 is an apocalyptic number.

It is an amenable number.

665016221 is a deficient number, since it is larger than the sum of its proper divisors (5479963).

665016221 is a wasteful number, since it uses less digits than its factorization.

665016221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4671.

The product of its (nonzero) digits is 4320, while the sum is 29.

The square root of 665016221 is about 25787.9084262373. The cubic root of 665016221 is about 872.8589704685.

Adding to 665016221 its reverse (122610566), we get a palindrome (787626787).

The spelling of 665016221 in words is "six hundred sixty-five million, sixteen thousand, two hundred twenty-one".