644956381 has 2 divisors, whose sum is σ = 644956382. Its totient is φ = 644956380.

The previous prime is 644956373. The next prime is 644956391. The reversal of 644956381 is 183659446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 458388100 + 186568281 = 21410^2 + 13659^2 .

It is a cyclic number.

It is not a de Polignac number, because 644956381 - 2³ = 644956373 is a prime.

It is a super-4 number, since 4×644956381⁴ (a number of 36 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644956321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322478190 + 322478191.

It is an arithmetic number, because the mean of its divisors is an integer number (322478191).

Almost surely, 2^644956381 is an apocalyptic number.

It is an amenable number.

644956381 is a deficient number, since it is larger than the sum of its proper divisors (1).

644956381 is an equidigital number, since it uses as much as digits as its factorization.

644956381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 622080, while the sum is 46.

The square root of 644956381 is about 25395.9914356577. The cubic root of 644956381 is about 863.9927826650.

It can be divided in two parts, 64495 and 6381, that added together give a triangular number (70876 = T₃₇₆).

The spelling of 644956381 in words is "six hundred forty-four million, nine hundred fifty-six thousand, three hundred eighty-one".