642812821 has 6 divisors (see below), whose sum is σ = 747761910. Its totient is φ = 550982376.

The previous prime is 642812791. The next prime is 642812827. The reversal of 642812821 is 128218246.

It can be written as a sum of positive squares in only one way, i.e., 549902500 + 92910321 = 23450^2 + 9639^2 .

It is not a de Polignac number, because 642812821 - 2¹⁵ = 642780053 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (642812827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 6559266 + ... + 6559363.

It is an arithmetic number, because the mean of its divisors is an integer number (124626985).

Almost surely, 2^642812821 is an apocalyptic number.

It is an amenable number.

642812821 is a deficient number, since it is larger than the sum of its proper divisors (104949089).

642812821 is a wasteful number, since it uses less digits than its factorization.

642812821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13118643 (or 13118636 counting only the distinct ones).

The product of its digits is 12288, while the sum is 34.

The square root of 642812821 is about 25353.7535879798. The cubic root of 642812821 is about 863.0345390814.

The spelling of 642812821 in words is "six hundred forty-two million, eight hundred twelve thousand, eight hundred twenty-one".