21217191 has 4 divisors (see below), whose sum is σ = 28289592. Its totient is φ = 14144792.

The previous prime is 21217187. The next prime is 21217193. The reversal of 21217191 is 19171212.

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 21217191 - 2² = 21217187 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217193) 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, 3536196 + ... + 3536201.

It is an arithmetic number, because the mean of its divisors is an integer number (7072398).

Almost surely, 2^21217191 is an apocalyptic number.

21217191 is a deficient number, since it is larger than the sum of its proper divisors (7072401).

21217191 is an equidigital number, since it uses as much as digits as its factorization.

21217191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7072400.

The product of its digits is 252, while the sum is 24.

The square root of 21217191 is about 4606.2122182982. The cubic root of 21217191 is about 276.8402898838.

The spelling of 21217191 in words is "twenty-one million, two hundred seventeen thousand, one hundred ninety-one".