21023906 has 8 divisors (see below), whose sum is σ = 31581084. Its totient is φ = 10496880.

The previous prime is 21023887. The next prime is 21023923. The reversal of 21023906 is 60932012.

It can be written as a sum of positive squares in 2 ways, for example, as 21022225 + 1681 = 4585^2 + 41^2 .

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

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5705 + ... + 8636.

Almost surely, 2^21023906 is an apocalyptic number.

21023906 is a deficient number, since it is larger than the sum of its proper divisors (10557178).

21023906 is a wasteful number, since it uses less digits than its factorization.

21023906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15076.

The product of its (nonzero) digits is 648, while the sum is 23.

The square root of 21023906 is about 4585.1833114937. The cubic root of 21023906 is about 275.9970681618.

Adding to 21023906 its reverse (60932012), we get a palindrome (81955918).

The spelling of 21023906 in words is "twenty-one million, twenty-three thousand, nine hundred six".