21406400 has 84 divisors (see below), whose sum is σ = 55842408. Its totient is φ = 8048640.

The previous prime is 21406397. The next prime is 21406457. The reversal of 21406400 is 460412.

It is a Harshad number since it is a multiple of its sum of digits (17).

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 26807 + ... + 27593.

Almost surely, 2^21406400 is an apocalyptic number.

21406400 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 21406400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27921204).

21406400 is an abundant number, since it is smaller than the sum of its proper divisors (34436008).

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

21406400 is a wasteful number, since it uses less digits than its factorization.

21406400 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 826 (or 811 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21406400 is about 4626.7050910988. The cubic root of 21406400 is about 277.6607839169.

Adding to 21406400 its reverse (460412), we get a palindrome (21866812).

The spelling of 21406400 in words is "twenty-one million, four hundred six thousand, four hundred".