21689397 has 8 divisors (see below), whose sum is σ = 32132480. Its totient is φ = 14459580.

The previous prime is 21689383. The next prime is 21689407. The reversal of 21689397 is 79398612.

It is not a de Polignac number, because 21689397 - 2¹⁵ = 21656629 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 (21689197) 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 7 ways as a sum of consecutive naturals, for example, 401629 + ... + 401682.

It is an arithmetic number, because the mean of its divisors is an integer number (4016560).

Almost surely, 2^21689397 is an apocalyptic number.

21689397 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21689397 is a deficient number, since it is larger than the sum of its proper divisors (10443083).

21689397 is an equidigital number, since it uses as much as digits as its factorization.

21689397 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 803320 (or 803314 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The square root of 21689397 is about 4657.1876706871. The cubic root of 21689397 is about 278.8790087016.

The spelling of 21689397 in words is "twenty-one million, six hundred eighty-nine thousand, three hundred ninety-seven".