21845217 has 4 divisors (see below), whose sum is σ = 29126960. Its totient is φ = 14563476.

The previous prime is 21845203. The next prime is 21845233. The reversal of 21845217 is 71254812.

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 21845217 - 2¹² = 21841121 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21845237) 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, 3640867 + ... + 3640872.

It is an arithmetic number, because the mean of its divisors is an integer number (7281740).

Almost surely, 2^21845217 is an apocalyptic number.

It is an amenable number.

21845217 is a deficient number, since it is larger than the sum of its proper divisors (7281743).

21845217 is an equidigital number, since it uses as much as digits as its factorization.

21845217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7281742.

The product of its digits is 4480, while the sum is 30.

The square root of 21845217 is about 4673.8867123626. The cubic root of 21845217 is about 279.5452524915.

The spelling of 21845217 in words is "twenty-one million, eight hundred forty-five thousand, two hundred seventeen".