21678918 has 24 divisors (see below), whose sum is σ = 44032968. Its totient is φ = 7114752.

The previous prime is 21678911. The next prime is 21678941. The reversal of 21678918 is 81987612.

It is a self number, because there is not a number n which added to its sum of digits gives 21678918.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21678911) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 112230 + ... + 112422.

It is an arithmetic number, because the mean of its divisors is an integer number (1834707).

Almost surely, 2^21678918 is an apocalyptic number.

21678918 is an abundant number, since it is smaller than the sum of its proper divisors (22354050).

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

21678918 is an equidigital number, since it uses as much as digits as its factorization.

21678918 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 488 (or 295 counting only the distinct ones).

The product of its digits is 48384, while the sum is 42.

The square root of 21678918 is about 4656.0624995805. The cubic root of 21678918 is about 278.8340889973.

The spelling of 21678918 in words is "twenty-one million, six hundred seventy-eight thousand, nine hundred eighteen".