646631221 has 2 divisors, whose sum is σ = 646631222. Its totient is φ = 646631220.

The previous prime is 646631173. The next prime is 646631257. The reversal of 646631221 is 122136646.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 613107121 + 33524100 = 24761^2 + 5790^2 .

It is a cyclic number.

It is not a de Polignac number, because 646631221 - 2¹¹ = 646629173 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (646631521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323315610 + 323315611.

It is an arithmetic number, because the mean of its divisors is an integer number (323315611).

Almost surely, 2^646631221 is an apocalyptic number.

It is an amenable number.

646631221 is a deficient number, since it is larger than the sum of its proper divisors (1).

646631221 is an equidigital number, since it uses as much as digits as its factorization.

646631221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10368, while the sum is 31.

The square root of 646631221 is about 25428.9445514359. The cubic root of 646631221 is about 864.7400160902.

Adding to 646631221 its reverse (122136646), we get a palindrome (768767867).

The spelling of 646631221 in words is "six hundred forty-six million, six hundred thirty-one thousand, two hundred twenty-one".