21405664 has 24 divisors (see below), whose sum is σ = 48163248. Its totient is φ = 9173760.

The previous prime is 21405661. The next prime is 21405667. The reversal of 21405664 is 46650412.

It is an interprime number because it is at equal distance from previous prime (21405661) and next prime (21405667).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21405661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47557 + ... + 48004.

It is an arithmetic number, because the mean of its divisors is an integer number (2006802).

Almost surely, 2^21405664 is an apocalyptic number.

It is an amenable number.

21405664 is an abundant number, since it is smaller than the sum of its proper divisors (26757584).

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

21405664 is an equidigital number, since it uses as much as digits as its factorization.

21405664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 95578 (or 95570 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 21405664 is about 4626.6255521708. The cubic root of 21405664 is about 277.6576016804.

The spelling of 21405664 in words is "twenty-one million, four hundred five thousand, six hundred sixty-four".