21421440 has 96 divisors (see below), whose sum is σ = 73990800. Its totient is φ = 5710848.

The previous prime is 21421427. The next prime is 21421451. The reversal of 21421440 is 4412412.

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 (18).

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 11 ways as a sum of consecutive naturals, for example, 3901 + ... + 7619.

Almost surely, 2^21421440 is an apocalyptic number.

21421440 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 21421440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36995400).

21421440 is an abundant number, since it is smaller than the sum of its proper divisors (52569360).

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

21421440 is a wasteful number, since it uses less digits than its factorization.

21421440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3744 (or 3729 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 18.

The square root of 21421440 is about 4628.3301524416. The cubic root of 21421440 is about 277.7257962583.

Adding to 21421440 its reverse (4412412), we get a palindrome (25833852).

Subtracting from 21421440 its reverse (4412412), we obtain a triangular number (17009028 = T₅₈₃₂).

The spelling of 21421440 in words is "twenty-one million, four hundred twenty-one thousand, four hundred forty".