21040051 has 4 divisors (see below), whose sum is σ = 21765600. Its totient is φ = 20314504.

The previous prime is 21040043. The next prime is 21040057. The reversal of 21040051 is 15004012.

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

It is a cyclic number.

It is not a de Polignac number, because 21040051 - 2³ = 21040043 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21040057) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 362731 + ... + 362788.

It is an arithmetic number, because the mean of its divisors is an integer number (5441400).

Almost surely, 2^21040051 is an apocalyptic number.

21040051 is a deficient number, since it is larger than the sum of its proper divisors (725549).

21040051 is an equidigital number, since it uses as much as digits as its factorization.

21040051 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 725548.

The product of its (nonzero) digits is 40, while the sum is 13.

The square root of 21040051 is about 4586.9435357327. The cubic root of 21040051 is about 276.0676993839.

Adding to 21040051 its reverse (15004012), we get a palindrome (36044063).

The spelling of 21040051 in words is "twenty-one million, forty thousand, fifty-one".