21553440 has 96 divisors (see below), whose sum is σ = 68838336. Its totient is φ = 5667840.

The previous prime is 21553421. The next prime is 21553453. The reversal of 21553440 is 4435512.

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21553440.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 39570 + ... + 40110.

It is an arithmetic number, because the mean of its divisors is an integer number (717066).

Almost surely, 2^21553440 is an apocalyptic number.

21553440 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 21553440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34419168).

21553440 is an abundant number, since it is smaller than the sum of its proper divisors (47284896).

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

21553440 is a wasteful number, since it uses less digits than its factorization.

21553440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 642 (or 634 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 24.

The square root of 21553440 is about 4642.5682547487. The cubic root of 21553440 is about 278.2950820139.

Adding to 21553440 its reverse (4435512), we get a palindrome (25988952).

The spelling of 21553440 in words is "twenty-one million, five hundred fifty-three thousand, four hundred forty".