20491921 has 4 divisors (see below), whose sum is σ = 20501172. Its totient is φ = 20482672.

The previous prime is 20491909. The next prime is 20491957. The reversal of 20491921 is 12919402.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12919402 = 2 ⋅6459701.

It can be written as a sum of positive squares in 2 ways, for example, as 7639696 + 12852225 = 2764^2 + 3585^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20491921 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 20491921.

It is not an unprimeable number, because it can be changed into a prime (20491901) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 891 + ... + 6463.

It is an arithmetic number, because the mean of its divisors is an integer number (5125293).

Almost surely, 2^20491921 is an apocalyptic number.

It is an amenable number.

20491921 is a deficient number, since it is larger than the sum of its proper divisors (9251).

20491921 is an equidigital number, since it uses as much as digits as its factorization.

20491921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9250.

The product of its (nonzero) digits is 1296, while the sum is 28.

The square root of 20491921 is about 4526.8003048511. The cubic root of 20491921 is about 273.6492261281.

It can be divided in two parts, 20491 and 921, that added together give a palindrome (21412).

The spelling of 20491921 in words is "twenty million, four hundred ninety-one thousand, nine hundred twenty-one".