21105421 has 16 divisors (see below), whose sum is σ = 22763520. Its totient is φ = 19522800.

The previous prime is 21105419. The next prime is 21105431. The reversal of 21105421 is 12450112.

It is a cyclic number.

It is not a de Polignac number, because 21105421 - 2¹ = 21105419 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21105395 and 21105404.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21105401) 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, 139696 + ... + 139846.

It is an arithmetic number, because the mean of its divisors is an integer number (1422720).

Almost surely, 2^21105421 is an apocalyptic number.

It is an amenable number.

21105421 is a deficient number, since it is larger than the sum of its proper divisors (1658099).

21105421 is a wasteful number, since it uses less digits than its factorization.

21105421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 336.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 21105421 is about 4594.0636695631. The cubic root of 21105421 is about 276.3533116178.

Adding to 21105421 its reverse (12450112), we get a palindrome (33555533).

The spelling of 21105421 in words is "twenty-one million, one hundred five thousand, four hundred twenty-one".