21391278 has 8 divisors (see below), whose sum is σ = 42782568. Its totient is φ = 7130424.

The previous prime is 21391267. The next prime is 21391301. The reversal of 21391278 is 87219312.

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

21391278 is an admirable number.

It is a plaindrome in base 16.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1782601 + ... + 1782612.

It is an arithmetic number, because the mean of its divisors is an integer number (5347821).

Almost surely, 2^21391278 is an apocalyptic number.

21391278 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21391278 is a wasteful number, since it uses less digits than its factorization.

21391278 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3565218.

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

The square root of 21391278 is about 4625.0705940558. The cubic root of 21391278 is about 277.5953864116.

The spelling of 21391278 in words is "twenty-one million, three hundred ninety-one thousand, two hundred seventy-eight".