6642021557 has 4 divisors (see below), whose sum is σ = 6642852780. Its totient is φ = 6641190336.

The previous prime is 6642021541. The next prime is 6642021559. The reversal of 6642021557 is 7551202466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 7551202466 = 2 ⋅3775601233.

It can be written as a sum of positive squares in 2 ways, for example, as 2834391121 + 3807630436 = 53239^2 + 61706^2 .

It is a cyclic number.

It is not a de Polignac number, because 6642021557 - 2⁴ = 6642021541 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 6642021557.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6642021559) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 403508 + ... + 419645.

It is an arithmetic number, because the mean of its divisors is an integer number (1660713195).

Almost surely, 2^6642021557 is an apocalyptic number.

It is an amenable number.

6642021557 is a deficient number, since it is larger than the sum of its proper divisors (831223).

6642021557 is an equidigital number, since it uses as much as digits as its factorization.

6642021557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 831222.

The product of its (nonzero) digits is 100800, while the sum is 38.

The square root of 6642021557 is about 81498.5984971521. The cubic root of 6642021557 is about 1879.7500004260.

The spelling of 6642021557 in words is "six billion, six hundred forty-two million, twenty-one thousand, five hundred fifty-seven".