21378965 has 4 divisors (see below), whose sum is σ = 25654764. Its totient is φ = 17103168.

The previous prime is 21378953. The next prime is 21378991. The reversal of 21378965 is 56987312.

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 9778129 + 11600836 = 3127^2 + 3406^2 .

It is a cyclic number.

It is not a de Polignac number, because 21378965 - 2⁴ = 21378949 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

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, 2137892 + ... + 2137901.

It is an arithmetic number, because the mean of its divisors is an integer number (6413691).

Almost surely, 2^21378965 is an apocalyptic number.

It is an amenable number.

21378965 is a deficient number, since it is larger than the sum of its proper divisors (4275799).

21378965 is an equidigital number, since it uses as much as digits as its factorization.

21378965 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4275798.

The product of its digits is 90720, while the sum is 41.

The square root of 21378965 is about 4623.7392876329. The cubic root of 21378965 is about 277.5421141072.

The spelling of 21378965 in words is "twenty-one million, three hundred seventy-eight thousand, nine hundred sixty-five".