21947 has 4 divisors (see below), whose sum is σ = 23256.
Its totient is φ = 20640.
The previous prime is 21943. The next prime is 21961. The reversal of 21947 is 74912.
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 21947 - 22 = 21943 is a prime.
It is a plaindrome in base 16.
It is a zygodrome in base 16.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21947.
It is not an unprimeable number, because it can be changed into a prime (21943) 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, 629 + ... + 662.
It is an arithmetic number, because the mean of its divisors is an integer number (5814).
221947 is an apocalyptic number.
21947 is a deficient number, since it is larger than the sum of its proper divisors (1309).
21947 is a wasteful number, since it uses less digits than its factorization.
21947 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 1308.
The product of its digits is 504, while the sum is 23.
The square root of 21947 is about 148.1451990447.
The cubic root of 21947 is about 27.9978739882.
The spelling of 21947 in words is "twenty-one thousand, nine hundred forty-seven".