8640221 has 2 divisors, whose sum is σ = 8640222. Its totient is φ = 8640220.

The previous prime is 8640211. The next prime is 8640241. The reversal of 8640221 is 1220468.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 8637721 + 2500 = 2939^2 + 50^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-8640221 is a prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (8640211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4320110 + 4320111.

It is an arithmetic number, because the mean of its divisors is an integer number (4320111).

Almost surely, 2^8640221 is an apocalyptic number.

It is an amenable number.

8640221 is a deficient number, since it is larger than the sum of its proper divisors (1).

8640221 is an equidigital number, since it uses as much as digits as its factorization.

8640221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 768, while the sum is 23.

The square root of 8640221 is about 2939.4252839628. The cubic root of 8640221 is about 205.1988631450.

Adding to 8640221 its reverse (1220468), we get a palindrome (9860689).

The spelling of 8640221 in words is "eight million, six hundred forty thousand, two hundred twenty-one".