6651221 has 2 divisors, whose sum is σ = 6651222. Its totient is φ = 6651220.

The previous prime is 6651217. The next prime is 6651223. The reversal of 6651221 is 1221566.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 4368100 + 2283121 = 2090^2 + 1511^2 .

It is a cyclic number.

It is not a de Polignac number, because 6651221 - 2² = 6651217 is a prime.

Together with 6651223, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6651223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3325610 + 3325611.

It is an arithmetic number, because the mean of its divisors is an integer number (3325611).

Almost surely, 2^6651221 is an apocalyptic number.

It is an amenable number.

6651221 is a deficient number, since it is larger than the sum of its proper divisors (1).

6651221 is an equidigital number, since it uses as much as digits as its factorization.

6651221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 720, while the sum is 23.

The square root of 6651221 is about 2578.9961225252. The cubic root of 6651221 is about 188.0617440924.

Adding to 6651221 its reverse (1221566), we get a palindrome (7872787).

The spelling of 6651221 in words is "six million, six hundred fifty-one thousand, two hundred twenty-one".