21381906 has 32 divisors (see below), whose sum is σ = 52633728. Its totient is φ = 5639040.

The previous prime is 21381901. The next prime is 21381929. The reversal of 21381906 is 60918312.

It is not an unprimeable number, because it can be changed into a prime (21381901) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 19035 + ... + 20126.

It is an arithmetic number, because the mean of its divisors is an integer number (1644804).

Almost surely, 2^21381906 is an apocalyptic number.

21381906 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

21381906 is an abundant number, since it is smaller than the sum of its proper divisors (31251822).

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

21381906 is a wasteful number, since it uses less digits than its factorization.

21381906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 39186.

The product of its (nonzero) digits is 2592, while the sum is 30.

The square root of 21381906 is about 4624.0573093334. The cubic root of 21381906 is about 277.5548402289.

The spelling of 21381906 in words is "twenty-one million, three hundred eighty-one thousand, nine hundred six".