21297440 has 24 divisors (see below), whose sum is σ = 50315580. Its totient is φ = 8518912.

The previous prime is 21297431. The next prime is 21297457. The reversal of 21297440 is 4479212.

It can be written as a sum of positive squares in 2 ways, for example, as 21270544 + 26896 = 4612^2 + 164^2 .

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, 66395 + ... + 66714.

Almost surely, 2^21297440 is an apocalyptic number.

21297440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21297440 is an abundant number, since it is smaller than the sum of its proper divisors (29018140).

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

21297440 is a wasteful number, since it uses less digits than its factorization.

21297440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133124 (or 133116 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 29.

The square root of 21297440 is about 4614.9149504623. The cubic root of 21297440 is about 277.1888783785.

The spelling of 21297440 in words is "twenty-one million, two hundred ninety-seven thousand, four hundred forty".