21217197 has 4 divisors (see below), whose sum is σ = 28289600. Its totient is φ = 14144796.

The previous prime is 21217193. The next prime is 21217199. The reversal of 21217197 is 79171212.

It is a happy number.

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 21217197 - 2² = 21217193 is a prime.

It is a Duffinian number.

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, 3536197 + ... + 3536202.

It is an arithmetic number, because the mean of its divisors is an integer number (7072400).

Almost surely, 2^21217197 is an apocalyptic number.

It is an amenable number.

21217197 is a deficient number, since it is larger than the sum of its proper divisors (7072403).

21217197 is an equidigital number, since it uses as much as digits as its factorization.

21217197 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7072402.

The product of its digits is 1764, while the sum is 30.

The square root of 21217197 is about 4606.2128695925. The cubic root of 21217197 is about 276.8403159797.

The spelling of 21217197 in words is "twenty-one million, two hundred seventeen thousand, one hundred ninety-seven".