21406380 has 48 divisors (see below), whose sum is σ = 60963840. Its totient is φ = 5610688.

The previous prime is 21406367. The next prime is 21406391. The reversal of 21406380 is 8360412.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21406380.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 517 + ... + 6563.

It is an arithmetic number, because the mean of its divisors is an integer number (1270080).

Almost surely, 2^21406380 is an apocalyptic number.

21406380 is a gapful number since it is divisible by the number (20) 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 21406380, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30481920).

21406380 is an abundant number, since it is smaller than the sum of its proper divisors (39557460).

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

21406380 is a wasteful number, since it uses less digits than its factorization.

21406380 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6118 (or 6116 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 24.

The square root of 21406380 is about 4626.7029297330. The cubic root of 21406380 is about 277.6606974440.

Adding to 21406380 its reverse (8360412), we get a palindrome (29766792).

The spelling of 21406380 in words is "twenty-one million, four hundred six thousand, three hundred eighty".