21185421 has 4 divisors (see below), whose sum is σ = 28247232. Its totient is φ = 14123612.

The previous prime is 21185419. The next prime is 21185441. The reversal of 21185421 is 12458112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21185421 - 2¹ = 21185419 is a prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21185391 and 21185400.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21185401) 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, 3530901 + ... + 3530906.

It is an arithmetic number, because the mean of its divisors is an integer number (7061808).

Almost surely, 2^21185421 is an apocalyptic number.

It is an amenable number.

21185421 is a deficient number, since it is larger than the sum of its proper divisors (7061811).

21185421 is an equidigital number, since it uses as much as digits as its factorization.

21185421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7061810.

The product of its digits is 640, while the sum is 24.

The square root of 21185421 is about 4602.7623227797. The cubic root of 21185421 is about 276.7020433465.

The spelling of 21185421 in words is "twenty-one million, one hundred eighty-five thousand, four hundred twenty-one".