644006261 has 2 divisors, whose sum is σ = 644006262. Its totient is φ = 644006260.

The previous prime is 644006249. The next prime is 644006263. The reversal of 644006261 is 162600446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 518700625 + 125305636 = 22775^2 + 11194^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644006261 is a prime.

Together with 644006263, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644006263) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322003130 + 322003131.

It is an arithmetic number, because the mean of its divisors is an integer number (322003131).

Almost surely, 2^644006261 is an apocalyptic number.

It is an amenable number.

644006261 is a deficient number, since it is larger than the sum of its proper divisors (1).

644006261 is an equidigital number, since it uses as much as digits as its factorization.

644006261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 29.

The square root of 644006261 is about 25377.2784395806. The cubic root of 644006261 is about 863.5683093831.

The spelling of 644006261 in words is "six hundred forty-four million, six thousand, two hundred sixty-one".