21278787 has 8 divisors (see below), whose sum is σ = 28416336. Its totient is φ = 14163552.

The previous prime is 21278773. The next prime is 21278797. The reversal of 21278787 is 78787212.

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

It is not a de Polignac number, because 21278787 - 2⁷ = 21278659 is a prime.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21278797) 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, 3208 + ... + 7269.

It is an arithmetic number, because the mean of its divisors is an integer number (3552042).

Almost surely, 2^21278787 is an apocalyptic number.

21278787 is a deficient number, since it is larger than the sum of its proper divisors (7137549).

21278787 is a wasteful number, since it uses less digits than its factorization.

21278787 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11157.

The product of its digits is 87808, while the sum is 42.

The square root of 21278787 is about 4612.8935604455. The cubic root of 21278787 is about 277.1079310228.

The spelling of 21278787 in words is "twenty-one million, two hundred seventy-eight thousand, seven hundred eighty-seven".