11721821 has 4 divisors (see below), whose sum is σ = 11914044. Its totient is φ = 11529600.

The previous prime is 11721817. The next prime is 11721833. The reversal of 11721821 is 12812711.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12812711 = 827 ⋅15493.

It can be written as a sum of positive squares in 2 ways, for example, as 4778596 + 6943225 = 2186^2 + 2635^2 .

It is a cyclic number.

It is not a de Polignac number, because 11721821 - 2² = 11721817 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (11721811) 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, 96020 + ... + 96141.

It is an arithmetic number, because the mean of its divisors is an integer number (2978511).

Almost surely, 2^11721821 is an apocalyptic number.

It is an amenable number.

11721821 is a deficient number, since it is larger than the sum of its proper divisors (192223).

11721821 is an equidigital number, since it uses as much as digits as its factorization.

11721821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 192222.

The product of its digits is 224, while the sum is 23.

The square root of 11721821 is about 3423.7145032844. The cubic root of 11721821 is about 227.1599137127.

The spelling of 11721821 in words is "eleven million, seven hundred twenty-one thousand, eight hundred twenty-one".