644006761 has 2 divisors, whose sum is σ = 644006762. Its totient is φ = 644006760.

The previous prime is 644006749. The next prime is 644006773. The reversal of 644006761 is 167600446.

It is a happy number.

It is a balanced prime because it is at equal distance from previous prime (644006749) and next prime (644006773).

It can be written as a sum of positive squares in only one way, i.e., 441798361 + 202208400 = 21019^2 + 14220^2 .

It is a cyclic number.

It is not a de Polignac number, because 644006761 - 2⁷ = 644006633 is a prime.

It is a super-2 number, since 2×644006761² = 829489416427422242, which contains 22 as substring.

It is equal to p_33498007 and since 644006761 and 33498007 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (644006261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322003380 + 322003381.

It is an arithmetic number, because the mean of its divisors is an integer number (322003381).

Almost surely, 2^644006761 is an apocalyptic number.

It is an amenable number.

644006761 is a deficient number, since it is larger than the sum of its proper divisors (1).

644006761 is an equidigital number, since it uses as much as digits as its factorization.

644006761 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 24192, while the sum is 34.

The square root of 644006761 is about 25377.2882909108. The cubic root of 644006761 is about 863.5685328716.

The spelling of 644006761 in words is "six hundred forty-four million, six thousand, seven hundred sixty-one".