21873821 has 2 divisors, whose sum is σ = 21873822. Its totient is φ = 21873820.

The previous prime is 21873809. The next prime is 21873823. The reversal of 21873821 is 12837812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21436900 + 436921 = 4630^2 + 661^2 .

It is a cyclic number.

It is not a de Polignac number, because 21873821 - 2¹⁰ = 21872797 is a prime.

Together with 21873823, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21873823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10936910 + 10936911.

It is an arithmetic number, because the mean of its divisors is an integer number (10936911).

Almost surely, 2^21873821 is an apocalyptic number.

It is an amenable number.

21873821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21873821 is an equidigital number, since it uses as much as digits as its factorization.

21873821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5376, while the sum is 32.

The square root of 21873821 is about 4676.9456913674. The cubic root of 21873821 is about 279.6672109186.

The spelling of 21873821 in words is "twenty-one million, eight hundred seventy-three thousand, eight hundred twenty-one".