21278113 has 4 divisors (see below), whose sum is σ = 21569668. Its totient is φ = 20986560.

The previous prime is 21278111. The next prime is 21278137. The reversal of 21278113 is 31187212.

It is a happy number.

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 12475024 + 8803089 = 3532^2 + 2967^2 .

It is a cyclic number.

It is not a de Polignac number, because 21278113 - 2¹ = 21278111 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21278111) 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 3 ways as a sum of consecutive naturals, for example, 145668 + ... + 145813.

It is an arithmetic number, because the mean of its divisors is an integer number (5392417).

Almost surely, 2^21278113 is an apocalyptic number.

It is an amenable number.

21278113 is a deficient number, since it is larger than the sum of its proper divisors (291555).

21278113 is an equidigital number, since it uses as much as digits as its factorization.

21278113 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 291554.

The product of its digits is 672, while the sum is 25.

The square root of 21278113 is about 4612.8205037699. The cubic root of 21278113 is about 277.1050052182.

Subtracting 21278113 from its reverse (31187212), we obtain a palindrome (9909099).

The spelling of 21278113 in words is "twenty-one million, two hundred seventy-eight thousand, one hundred thirteen".