21616997 has 4 divisors (see below), whose sum is σ = 21971436. Its totient is φ = 21262560.

The previous prime is 21616967. The next prime is 21616999. The reversal of 21616997 is 79961612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3690241 + 17926756 = 1921^2 + 4234^2 .

It is a cyclic number.

It is not a de Polignac number, because 21616997 - 2¹⁰ = 21615973 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 (21616999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 177128 + ... + 177249.

It is an arithmetic number, because the mean of its divisors is an integer number (5492859).

Almost surely, 2^21616997 is an apocalyptic number.

It is an amenable number.

21616997 is a deficient number, since it is larger than the sum of its proper divisors (354439).

21616997 is an equidigital number, since it uses as much as digits as its factorization.

21616997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 354438.

The product of its digits is 40824, while the sum is 41.

The square root of 21616997 is about 4649.4082419164. The cubic root of 21616997 is about 278.5683600175.

The spelling of 21616997 in words is "twenty-one million, six hundred sixteen thousand, nine hundred ninety-seven".