21357440 has 128 divisors (see below), whose sum is σ = 58605120. Its totient is φ = 7372800.

The previous prime is 21357431. The next prime is 21357443. The reversal of 21357440 is 4475312.

It is a tau number, because it is divible by the number of its divisors (128).

It is a super-2 number, since 2×21357440² = 912280486707200, which contains 22 as substring.

It is a hoax number, since the sum of its digits (26) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (26).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21357443) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 141365 + ... + 141515.

Almost surely, 2^21357440 is an apocalyptic number.

21357440 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 21357440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29302560).

21357440 is an abundant number, since it is smaller than the sum of its proper divisors (37247680).

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

21357440 is a wasteful number, since it uses less digits than its factorization.

21357440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 200 (or 188 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 26.

The square root of 21357440 is about 4621.4110399314. The cubic root of 21357440 is about 277.4489368479.

The spelling of 21357440 in words is "twenty-one million, three hundred fifty-seven thousand, four hundred forty".