21378981 has 16 divisors (see below), whose sum is σ = 31280256. Its totient is φ = 12906816.

The previous prime is 21378953. The next prime is 21378991. The reversal of 21378981 is 18987312.

It is not a de Polignac number, because 21378981 - 2⁵ = 21378949 is a prime.

It is a super-2 number, since 2×21378981² = 914121657196722, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21378991) 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 15 ways as a sum of consecutive naturals, for example, 3105 + ... + 7238.

It is an arithmetic number, because the mean of its divisors is an integer number (1955016).

Almost surely, 2^21378981 is an apocalyptic number.

It is an amenable number.

21378981 is a deficient number, since it is larger than the sum of its proper divisors (9901275).

21378981 is a wasteful number, since it uses less digits than its factorization.

21378981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10412.

The product of its digits is 24192, while the sum is 39.

The square root of 21378981 is about 4623.7410178339. The cubic root of 21378981 is about 277.5421833446.

The spelling of 21378981 in words is "twenty-one million, three hundred seventy-eight thousand, nine hundred eighty-one".