21621408 has 24 divisors (see below), whose sum is σ = 56756448. Its totient is φ = 7207104.

The previous prime is 21621401. The next prime is 21621409. The reversal of 21621408 is 80412612.

It is a tau number, because it is divible by the number of its divisors (24).

It is a Harshad number since it is a multiple of its sum of digits (24).

It is not an unprimeable number, because it can be changed into a prime (21621401) by changing a digit.

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, 112516 + ... + 112707.

It is an arithmetic number, because the mean of its divisors is an integer number (2364852).

Almost surely, 2^21621408 is an apocalyptic number.

It is an amenable number.

21621408 is an abundant number, since it is smaller than the sum of its proper divisors (35135040).

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

21621408 is a wasteful number, since it uses less digits than its factorization.

21621408 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 225236 (or 225228 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 24.

The square root of 21621408 is about 4649.8825791626. The cubic root of 21621408 is about 278.5873062426.

It can be divided in two parts, 2162 and 1408, that added together give a triangular number (3570 = T₈₄).

The spelling of 21621408 in words is "twenty-one million, six hundred twenty-one thousand, four hundred eight".