21432640 has 28 divisors (see below), whose sum is σ = 51037236. Its totient is φ = 8572928.

The previous prime is 21432629. The next prime is 21432661. The reversal of 21432640 is 4623412.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 3182656 + 18249984 = 1784^2 + 4272^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33169 + ... + 33808.

Almost surely, 2^21432640 is an apocalyptic number.

21432640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21432640 is an abundant number, since it is smaller than the sum of its proper divisors (29604596).

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

21432640 is an equidigital number, since it uses as much as digits as its factorization.

21432640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66994 (or 66984 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 22.

The square root of 21432640 is about 4629.5399339459. The cubic root of 21432640 is about 277.7741899388.

The spelling of 21432640 in words is "twenty-one million, four hundred thirty-two thousand, six hundred forty".