11821 has 2 divisors, whose sum is σ = 11822. Its totient is φ = 11820.

The previous prime is 11813. The next prime is 11827. The reversal of 11821 is 12811.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 8100 + 3721 = 90^2 + 61^2 .

It is a cyclic number.

It is not a de Polignac number, because 11821 - 2³ = 11813 is a prime.

It is equal to p₁₄₁₇ and since 11821 and 1417 have the same sum of digits, it is a Honaker prime.

It is a plaindrome in base 14.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (11827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5910 + 5911.

It is an arithmetic number, because the mean of its divisors is an integer number (5911).

2¹¹⁸²¹ is an apocalyptic number.

It is an amenable number.

11821 is a deficient number, since it is larger than the sum of its proper divisors (1).

11821 is an equidigital number, since it uses as much as digits as its factorization.

11821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 16, while the sum is 13.

The square root of 11821 is about 108.7244222794. The cubic root of 11821 is about 22.7798786262.

Subtracting 11821 from its reverse (12811), we obtain a triangular number (990 = T₄₄).

The spelling of 11821 in words is "eleven thousand, eight hundred twenty-one".