21381408 has 120 divisors (see below), whose sum is σ = 64307628. Its totient is φ = 6967296.

The previous prime is 21381407. The next prime is 21381433. The reversal of 21381408 is 80418312.

It can be written as a sum of positive squares in 2 ways, for example, as 19607184 + 1774224 = 4428^2 + 1332^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21381407) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 189160 + ... + 189272.

Almost surely, 2^21381408 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21381408, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32153814).

21381408 is an abundant number, since it is smaller than the sum of its proper divisors (42926220).

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

21381408 is a wasteful number, since it uses less digits than its factorization.

21381408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 208 (or 191 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 27.

The square root of 21381408 is about 4624.0034602063. The cubic root of 21381408 is about 277.5526853948.

The spelling of 21381408 in words is "twenty-one million, three hundred eighty-one thousand, four hundred eight".