644868481 has 2 divisors, whose sum is σ = 644868482. Its totient is φ = 644868480.

The previous prime is 644868439. The next prime is 644868487. The reversal of 644868481 is 184868446.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 596092225 + 48776256 = 24415^2 + 6984^2 .

It is a cyclic number.

It is not a de Polignac number, because 644868481 - 2¹⁷ = 644737409 is a prime.

It is a super-2 number, since 2×644868481² = 831710715574494722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (644868487) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322434240 + 322434241.

It is an arithmetic number, because the mean of its divisors is an integer number (322434241).

Almost surely, 2^644868481 is an apocalyptic number.

It is an amenable number.

644868481 is a deficient number, since it is larger than the sum of its proper divisors (1).

644868481 is an equidigital number, since it uses as much as digits as its factorization.

644868481 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1179648, while the sum is 49.

The square root of 644868481 is about 25394.2607886113. The cubic root of 644868481 is about 863.9535301832.

The spelling of 644868481 in words is "six hundred forty-four million, eight hundred sixty-eight thousand, four hundred eighty-one".