644216381 has 2 divisors, whose sum is σ = 644216382. Its totient is φ = 644216380.

The previous prime is 644216371. The next prime is 644216399. The reversal of 644216381 is 183612446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 580376281 + 63840100 = 24091^2 + 7990^2 .

It is a cyclic number.

It is not a de Polignac number, because 644216381 - 2⁶ = 644216317 is a prime.

It is a super-2 number, since 2×644216381² = 830029491097474322, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644216371) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322108190 + 322108191.

It is an arithmetic number, because the mean of its divisors is an integer number (322108191).

Almost surely, 2^644216381 is an apocalyptic number.

It is an amenable number.

644216381 is a deficient number, since it is larger than the sum of its proper divisors (1).

644216381 is an equidigital number, since it uses as much as digits as its factorization.

644216381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 27648, while the sum is 35.

The square root of 644216381 is about 25381.4180257920. The cubic root of 644216381 is about 863.6622180159.

The spelling of 644216381 in words is "six hundred forty-four million, two hundred sixteen thousand, three hundred eighty-one".