21193921 has 12 divisors (see below), whose sum is σ = 25075440. Its totient is φ = 17855880.

The previous prime is 21193919. The next prime is 21193927. The reversal of 21193921 is 12939112.

It is not a de Polignac number, because 21193921 - 2¹ = 21193919 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21193921.

It is not an unprimeable number, because it can be changed into a prime (21193927) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 775 + ... + 6556.

It is an arithmetic number, because the mean of its divisors is an integer number (2089620).

Almost surely, 2^21193921 is an apocalyptic number.

It is an amenable number.

21193921 is a deficient number, since it is larger than the sum of its proper divisors (3881519).

21193921 is an equidigital number, since it uses as much as digits as its factorization.

21193921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7404 (or 7397 counting only the distinct ones).

The product of its digits is 972, while the sum is 28.

The square root of 21193921 is about 4603.6855887430. The cubic root of 21193921 is about 276.7390444660.

The spelling of 21193921 in words is "twenty-one million, one hundred ninety-three thousand, nine hundred twenty-one".