645122761 has 2 divisors, whose sum is σ = 645122762. Its totient is φ = 645122760.

The previous prime is 645122759. The next prime is 645122773. The reversal of 645122761 is 167221546.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 582015625 + 63107136 = 24125^2 + 7944^2 .

It is a cyclic number.

It is not a de Polignac number, because 645122761 - 2¹ = 645122759 is a prime.

Together with 645122759, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (645128761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322561380 + 322561381.

It is an arithmetic number, because the mean of its divisors is an integer number (322561381).

Almost surely, 2^645122761 is an apocalyptic number.

It is an amenable number.

645122761 is a deficient number, since it is larger than the sum of its proper divisors (1).

645122761 is an equidigital number, since it uses as much as digits as its factorization.

645122761 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20160, while the sum is 34.

The square root of 645122761 is about 25399.2669382406. The cubic root of 645122761 is about 864.0670712857.

The spelling of 645122761 in words is "six hundred forty-five million, one hundred twenty-two thousand, seven hundred sixty-one".