21537440 has 24 divisors (see below), whose sum is σ = 50882580. Its totient is φ = 8614912.

The previous prime is 21537427. The next prime is 21537473. The reversal of 21537440 is 4473512.

It can be written as a sum of positive squares in 2 ways, for example, as 21492496 + 44944 = 4636^2 + 212^2 .

It is a super-2 number, since 2×21537440² = 927722643507200, which contains 22 as substring.

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, 67145 + ... + 67464.

Almost surely, 2^21537440 is an apocalyptic number.

21537440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21537440 is an abundant number, since it is smaller than the sum of its proper divisors (29345140).

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

21537440 is a wasteful number, since it uses less digits than its factorization.

21537440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 134624 (or 134616 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 26.

The square root of 21537440 is about 4640.8447506893. The cubic root of 21537440 is about 278.2262016932.

The spelling of 21537440 in words is "twenty-one million, five hundred thirty-seven thousand, four hundred forty".