644135440381 has 2 divisors, whose sum is σ = 644135440382. Its totient is φ = 644135440380.

The previous prime is 644135440337. The next prime is 644135440387. The reversal of 644135440381 is 183044531446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 615416715225 + 28718725156 = 784485^2 + 169466^2 .

It is a cyclic number.

It is not a de Polignac number, because 644135440381 - 2¹⁷ = 644135309309 is a prime.

It is a super-2 number, since 2×644135440381² (a number of 24 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644135440387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322067720190 + 322067720191.

It is an arithmetic number, because the mean of its divisors is an integer number (322067720191).

Almost surely, 2^644135440381 is an apocalyptic number.

It is an amenable number.

644135440381 is a deficient number, since it is larger than the sum of its proper divisors (1).

644135440381 is an equidigital number, since it uses as much as digits as its factorization.

644135440381 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 552960, while the sum is 43.

The spelling of 644135440381 in words is "six hundred forty-four billion, one hundred thirty-five million, four hundred forty thousand, three hundred eighty-one".