21908217 has 4 divisors (see below), whose sum is σ = 29210960. Its totient is φ = 14605476.

The previous prime is 21908209. The next prime is 21908219. The reversal of 21908217 is 71280912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21908217 - 2³ = 21908209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21908219) 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, 3651367 + ... + 3651372.

It is an arithmetic number, because the mean of its divisors is an integer number (7302740).

Almost surely, 2^21908217 is an apocalyptic number.

It is an amenable number.

21908217 is a deficient number, since it is larger than the sum of its proper divisors (7302743).

21908217 is an equidigital number, since it uses as much as digits as its factorization.

21908217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7302742.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 21908217 is about 4680.6214331005. The cubic root of 21908217 is about 279.8137238924.

The spelling of 21908217 in words is "twenty-one million, nine hundred eight thousand, two hundred seventeen".