21278913 has 8 divisors (see below), whose sum is σ = 28771776. Its totient is φ = 13986000.

The previous prime is 21278911. The next prime is 21278923. The reversal of 21278913 is 31987212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21278913 - 2¹ = 21278911 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21278911) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 49738 + ... + 50163.

It is an arithmetic number, because the mean of its divisors is an integer number (3596472).

Almost surely, 2^21278913 is an apocalyptic number.

It is an amenable number.

21278913 is a deficient number, since it is larger than the sum of its proper divisors (7492863).

21278913 is an equidigital number, since it uses as much as digits as its factorization.

21278913 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 99975.

The product of its digits is 6048, while the sum is 33.

The square root of 21278913 is about 4612.9072177966. The cubic root of 21278913 is about 277.1084779764.

The spelling of 21278913 in words is "twenty-one million, two hundred seventy-eight thousand, nine hundred thirteen".