21403440 has 140 divisors (see below), whose sum is σ = 74813664. Its totient is φ = 5692032.

The previous prime is 21403439. The next prime is 21403441. The reversal of 21403440 is 4430412.

It is an interprime number because it is at equal distance from previous prime (21403439) and next prime (21403441).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (21403441) by changing a digit.

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 27 ways as a sum of consecutive naturals, for example, 58137 + ... + 58503.

Almost surely, 2^21403440 is an apocalyptic number.

21403440 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 21403440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37406832).

21403440 is an abundant number, since it is smaller than the sum of its proper divisors (53410224).

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

21403440 is an equidigital number, since it uses as much as digits as its factorization.

21403440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 398 (or 377 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 21403440 is about 4626.3851979704. The cubic root of 21403440 is about 277.6479853488.

Adding to 21403440 its reverse (4430412), we get a palindrome (25833852).

The spelling of 21403440 in words is "twenty-one million, four hundred three thousand, four hundred forty".