21378721 has 8 divisors (see below), whose sum is σ = 26312384. Its totient is φ = 16914960.

The previous prime is 21378701. The next prime is 21378733. The reversal of 21378721 is 12787312.

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 21378721 - 2⁷ = 21378593 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21378701) 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, 117375 + ... + 117556.

It is an arithmetic number, because the mean of its divisors is an integer number (3289048).

Almost surely, 2^21378721 is an apocalyptic number.

It is an amenable number.

21378721 is a deficient number, since it is larger than the sum of its proper divisors (4933663).

21378721 is a wasteful number, since it uses less digits than its factorization.

21378721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 234951.

The product of its digits is 4704, while the sum is 31.

The square root of 21378721 is about 4623.7129019869. The cubic root of 21378721 is about 277.5410582324.

The spelling of 21378721 in words is "twenty-one million, three hundred seventy-eight thousand, seven hundred twenty-one".