21051906 has 8 divisors (see below), whose sum is σ = 42103824. Its totient is φ = 7017300.

The previous prime is 21051887. The next prime is 21051907. The reversal of 21051906 is 60915012.

It is a sphenic number, since it is the product of 3 distinct primes.

21051906 is an admirable number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21051907) 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, 1754320 + ... + 1754331.

It is an arithmetic number, because the mean of its divisors is an integer number (5262978).

Almost surely, 2^21051906 is an apocalyptic number.

21051906 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21051906 is a wasteful number, since it uses less digits than its factorization.

21051906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3508656.

The product of its (nonzero) digits is 540, while the sum is 24.

The square root of 21051906 is about 4588.2356085973. The cubic root of 21051906 is about 276.1195396905.

Adding to 21051906 its reverse (60915012), we get a palindrome (81966918).

The spelling of 21051906 in words is "twenty-one million, fifty-one thousand, nine hundred six".