21538440 has 384 divisors, whose sum is σ = 93571200. Its totient is φ = 4354560.

The previous prime is 21538427. The next prime is 21538453. The reversal of 21538440 is 4483512.

21538440 is a `hidden beast` number, since 215 + 3 + 8 + 440 = 666.

It is an interprime number because it is at equal distance from previous prime (21538427) and next prime (21538453).

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

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 582102 + ... + 582138.

It is an arithmetic number, because the mean of its divisors is an integer number (243675).

Almost surely, 2^21538440 is an apocalyptic number.

21538440 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 21538440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (46785600).

21538440 is an abundant number, since it is smaller than the sum of its proper divisors (72032760).

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

21538440 is a wasteful number, since it uses less digits than its factorization.

21538440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82 (or 65 counting only the distinct ones).

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

The square root of 21538440 is about 4640.9524884446. The cubic root of 21538440 is about 278.2305077125.

The spelling of 21538440 in words is "twenty-one million, five hundred thirty-eight thousand, four hundred forty".