21745440 has 72 divisors (see below), whose sum is σ = 74211228. Its totient is φ = 5798400.

The previous prime is 21745433. The next prime is 21745441. The reversal of 21745440 is 4454712.

21745440 is a `hidden beast` number, since 217 + 4 + 5 + 440 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 20034576 + 1710864 = 4476^2 + 1308^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is not an unprimeable number, because it can be changed into a prime (21745441) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6111 + ... + 8990.

Almost surely, 2^21745440 is an apocalyptic number.

21745440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21745440 is an abundant number, since it is smaller than the sum of its proper divisors (52465788).

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

21745440 is a wasteful number, since it uses less digits than its factorization.

21745440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15122 (or 15111 counting only the distinct ones).

The product of its (nonzero) digits is 4480, while the sum is 27.

The square root of 21745440 is about 4663.2006176016. The cubic root of 21745440 is about 279.1189996088.

The spelling of 21745440 in words is "twenty-one million, seven hundred forty-five thousand, four hundred forty".