21187908 has 72 divisors (see below), whose sum is σ = 62008128. Its totient is φ = 5974848.

The previous prime is 21187897. The next prime is 21187913. The reversal of 21187908 is 80978112.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 20410 + ... + 21422.

It is an arithmetic number, because the mean of its divisors is an integer number (861224).

Almost surely, 2^21187908 is an apocalyptic number.

21187908 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21187908, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31004064).

21187908 is an abundant number, since it is smaller than the sum of its proper divisors (40820220).

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

21187908 is a wasteful number, since it uses less digits than its factorization.

21187908 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1113 (or 1108 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 21187908 is about 4603.0324787036. The cubic root of 21187908 is about 276.7128704628.

The spelling of 21187908 in words is "twenty-one million, one hundred eighty-seven thousand, nine hundred eight".