21051947057 has 4 divisors (see below), whose sum is σ = 21059778660. Its totient is φ = 21044115456.

The previous prime is 21051947053. The next prime is 21051947069. The reversal of 21051947057 is 75074915012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1465664656 + 19586282401 = 38284^2 + 139951^2 .

It is a cyclic number.

It is not a de Polignac number, because 21051947057 - 2² = 21051947053 is a prime.

It is a super-2 number, since 2×21051947057² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21051947053) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3911768 + ... + 3917145.

It is an arithmetic number, because the mean of its divisors is an integer number (5264944665).

Almost surely, 2^21051947057 is an apocalyptic number.

It is an amenable number.

21051947057 is a deficient number, since it is larger than the sum of its proper divisors (7831603).

21051947057 is an equidigital number, since it uses as much as digits as its factorization.

21051947057 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7831602.

The product of its (nonzero) digits is 88200, while the sum is 41.

The spelling of 21051947057 in words is "twenty-one billion, fifty-one million, nine hundred forty-seven thousand, fifty-seven".