644692261 has 2 divisors, whose sum is σ = 644692262. Its totient is φ = 644692260.

The previous prime is 644692199. The next prime is 644692267. The reversal of 644692261 is 162296446.

It is a happy number.

644692261 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 376748100 + 267944161 = 19410^2 + 16369^2 .

It is a cyclic number.

It is not a de Polignac number, because 644692261 - 2¹³ = 644684069 is a prime.

It is a super-2 number, since 2×644692261² = 831256222786584242, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644692267) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322346130 + 322346131.

It is an arithmetic number, because the mean of its divisors is an integer number (322346131).

Almost surely, 2^644692261 is an apocalyptic number.

It is an amenable number.

644692261 is a deficient number, since it is larger than the sum of its proper divisors (1).

644692261 is an equidigital number, since it uses as much as digits as its factorization.

644692261 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 124416, while the sum is 40.

The square root of 644692261 is about 25390.7908699197. The cubic root of 644692261 is about 863.8748269201.

The spelling of 644692261 in words is "six hundred forty-four million, six hundred ninety-two thousand, two hundred sixty-one".