21043638 has 120 divisors (see below), whose sum is σ = 60086664. Its totient is φ = 5443200.

The previous prime is 21043613. The next prime is 21043661. The reversal of 21043638 is 83634012.

It is a happy number.

21043638 is a `hidden beast` number, since 21 + 0 + 4 + 3 + 638 = 666.

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

It is a congruent number.

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 59 ways as a sum of consecutive naturals, for example, 87198 + ... + 87438.

Almost surely, 2^21043638 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21043638, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30043332).

21043638 is an abundant number, since it is smaller than the sum of its proper divisors (39043026).

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

21043638 is a wasteful number, since it uses less digits than its factorization.

21043638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 280 (or 264 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 21043638 is about 4587.3345201762. The cubic root of 21043638 is about 276.0833869024.

The spelling of 21043638 in words is "twenty-one million, forty-three thousand, six hundred thirty-eight".