21217897 has 8 divisors (see below), whose sum is σ = 21625344. Its totient is φ = 20814528.

The previous prime is 21217849. The next prime is 21217907. The reversal of 21217897 is 79871212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21217897 - 2¹⁹ = 20693609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21217837) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10728 + ... + 12550.

It is an arithmetic number, because the mean of its divisors is an integer number (2703168).

Almost surely, 2^21217897 is an apocalyptic number.

It is an amenable number.

21217897 is a deficient number, since it is larger than the sum of its proper divisors (407447).

21217897 is a wasteful number, since it uses less digits than its factorization.

21217897 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2039.

The product of its digits is 14112, while the sum is 37.

The square root of 21217897 is about 4606.2888532961. The cubic root of 21217897 is about 276.8433604612.

The spelling of 21217897 in words is "twenty-one million, two hundred seventeen thousand, eight hundred ninety-seven".