21388207 has 4 divisors (see below), whose sum is σ = 21418120. Its totient is φ = 21358296.

The previous prime is 21388201. The next prime is 21388219. The reversal of 21388207 is 70288312.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21388207 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21388201) 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, 13857 + ... + 15322.

It is an arithmetic number, because the mean of its divisors is an integer number (5354530).

Almost surely, 2^21388207 is an apocalyptic number.

21388207 is a deficient number, since it is larger than the sum of its proper divisors (29913).

21388207 is an equidigital number, since it uses as much as digits as its factorization.

21388207 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29912.

The product of its (nonzero) digits is 5376, while the sum is 31.

The square root of 21388207 is about 4624.7385872068. The cubic root of 21388207 is about 277.5821016166.

The spelling of 21388207 in words is "twenty-one million, three hundred eighty-eight thousand, two hundred seven".