21400640 has 28 divisors (see below), whose sum is σ = 50961036. Its totient is φ = 8560128.

The previous prime is 21400597. The next prime is 21400667. The reversal of 21400640 is 4600412.

It can be written as a sum of positive squares in 2 ways, for example, as 3013696 + 18386944 = 1736^2 + 4288^2 .

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, 33119 + ... + 33758.

It is an arithmetic number, because the mean of its divisors is an integer number (1820037).

Almost surely, 2^21400640 is an apocalyptic number.

21400640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21400640 is an abundant number, since it is smaller than the sum of its proper divisors (29560396).

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

21400640 is an equidigital number, since it uses as much as digits as its factorization.

21400640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66894 (or 66884 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21400640 is about 4626.0825760032. The cubic root of 21400640 is about 277.6358775091.

The spelling of 21400640 in words is "twenty-one million, four hundred thousand, six hundred forty".