21432440 has 16 divisors (see below), whose sum is σ = 48223080. Its totient is φ = 8572960.

The previous prime is 21432413. The next prime is 21432443. The reversal of 21432440 is 4423412.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21432443) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 267866 + ... + 267945.

Almost surely, 2^21432440 is an apocalyptic number.

21432440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21432440 is an abundant number, since it is smaller than the sum of its proper divisors (26790640).

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

21432440 is a wasteful number, since it uses less digits than its factorization.

21432440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 535822 (or 535818 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 20.

The square root of 21432440 is about 4629.5183334770. The cubic root of 21432440 is about 277.7733259138.

Adding to 21432440 its reverse (4423412), we get a palindrome (25855852).

Subtracting from 21432440 its reverse (4423412), we obtain a triangular number (17009028 = T₅₈₃₂).

The spelling of 21432440 in words is "twenty-one million, four hundred thirty-two thousand, four hundred forty".