21907 has 4 divisors (see below), whose sum is σ = 23080.
Its totient is φ = 20736.
The previous prime is 21893. The next prime is 21911. The reversal of 21907 is 70912.
It can be divided in two parts, 2190 and 7, that added together give a cube (2197 = 133).
It is a semiprime because it is the product of two primes.
It is a 8-Lehmer number, since φ(21907) divides (21907-1)8.
It is a cyclic number.
It is a de Polignac number, because none of the positive numbers 2k-21907 is a prime.
It is a Harshad number since it is a multiple of its sum of digits (19), and also a Moran number because the ratio is a prime number: 1153 = 21907 / (2 + 1 + 9 + 0 + 7).
It is a Duffinian number.
It is not an unprimeable number, because it can be changed into a prime (21937) 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, 558 + ... + 595.
It is an arithmetic number, because the mean of its divisors is an integer number (5770).
221907 is an apocalyptic number.
21907 is a deficient number, since it is larger than the sum of its proper divisors (1173).
21907 is a wasteful number, since it uses less digits than its factorization.
21907 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 1172.
The product of its (nonzero) digits is 126, while the sum is 19.
The square root of 21907 is about 148.0101347881.
The cubic root of 21907 is about 27.9808542585.
The spelling of 21907 in words is "twenty-one thousand, nine hundred seven".