21621440 has 28 divisors (see below), whose sum is σ = 51486816. Its totient is φ = 8648448.

The previous prime is 21621437. The next prime is 21621463. The reversal of 21621440 is 4412612.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33464 + ... + 34103.

Almost surely, 2^21621440 is an apocalyptic number.

21621440 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21621440 is an abundant number, since it is smaller than the sum of its proper divisors (29865376).

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

21621440 is an equidigital number, since it uses as much as digits as its factorization.

21621440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67584 (or 67574 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21621440 is about 4649.8860201084. The cubic root of 21621440 is about 278.5874436803.

The spelling of 21621440 in words is "twenty-one million, six hundred twenty-one thousand, four hundred forty".