21405697 has 4 divisors (see below), whose sum is σ = 21415680. Its totient is φ = 21395716.

The previous prime is 21405691. The next prime is 21405733. The reversal of 21405697 is 79650412.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21405697 - 2⁷ = 21405569 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21405691) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 313 + ... + 6550.

It is an arithmetic number, because the mean of its divisors is an integer number (5353920).

It is a Proth number, since it is equal to 2613 ⋅ 2¹³ + 1 and 2613 < 2¹³.

Almost surely, 2^21405697 is an apocalyptic number.

It is an amenable number.

21405697 is a deficient number, since it is larger than the sum of its proper divisors (9983).

21405697 is an equidigital number, since it uses as much as digits as its factorization.

21405697 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9982.

The product of its (nonzero) digits is 15120, while the sum is 34.

The square root of 21405697 is about 4626.6291184836. The cubic root of 21405697 is about 277.6577443638.

The spelling of 21405697 in words is "twenty-one million, four hundred five thousand, six hundred ninety-seven".