21408621 has 16 divisors (see below), whose sum is σ = 31248000. Its totient is φ = 12957120.

The previous prime is 21408613. The next prime is 21408623. The reversal of 21408621 is 12680412.

It is not a de Polignac number, because 21408621 - 2³ = 21408613 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21408591 and 21408600.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21408623) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2121 + ... + 6878.

It is an arithmetic number, because the mean of its divisors is an integer number (1953000).

Almost surely, 2^21408621 is an apocalyptic number.

It is an amenable number.

21408621 is a deficient number, since it is larger than the sum of its proper divisors (9839379).

21408621 is a wasteful number, since it uses less digits than its factorization.

21408621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9076.

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

The square root of 21408621 is about 4626.9451044939. The cubic root of 21408621 is about 277.6703863921.

The spelling of 21408621 in words is "twenty-one million, four hundred eight thousand, six hundred twenty-one".