21571440 has 80 divisors (see below), whose sum is σ = 72959616. Its totient is φ = 5228800.

The previous prime is 21571439. The next prime is 21571463. The reversal of 21571440 is 4417512.

It is a tau number, because it is divible by the number of its divisors (80).

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 21571440.

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 15 ways as a sum of consecutive naturals, for example, 1446 + ... + 6725.

Almost surely, 2^21571440 is an apocalyptic number.

21571440 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 21571440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36479808).

21571440 is an abundant number, since it is smaller than the sum of its proper divisors (51388176).

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

21571440 is a wasteful number, since it uses less digits than its factorization.

21571440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8198 (or 8192 counting only the distinct ones).

The product of its (nonzero) digits is 1120, while the sum is 24.

The square root of 21571440 is about 4644.5064323349. The cubic root of 21571440 is about 278.3725316406.

Adding to 21571440 its reverse (4417512), we get a palindrome (25988952).

The spelling of 21571440 in words is "twenty-one million, five hundred seventy-one thousand, four hundred forty".