21405384 has 288 divisors, whose sum is σ = 81332160. Its totient is φ = 5132160.

The previous prime is 21405383. The next prime is 21405401. The reversal of 21405384 is 48350412.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405383) by changing a digit.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 1646562 + ... + 1646574.

Almost surely, 2^21405384 is an apocalyptic number.

21405384 is a gapful number since it is divisible by the number (24) 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 21405384, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40666080).

21405384 is an abundant number, since it is smaller than the sum of its proper divisors (59926776).

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

21405384 is a wasteful number, since it uses less digits than its factorization.

21405384 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63 (or 36 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 27.

The square root of 21405384 is about 4626.5952924370. The cubic root of 21405384 is about 277.6563910278.

Adding to 21405384 its reverse (48350412), we get a palindrome (69755796).

The spelling of 21405384 in words is "twenty-one million, four hundred five thousand, three hundred eighty-four".