21806819 has 2 divisors, whose sum is σ = 21806820. Its totient is φ = 21806818.

The previous prime is 21806803. The next prime is 21806831. The reversal of 21806819 is 91860812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21806819 - 2⁴ = 21806803 is a prime.

It is a super-3 number, since 3×21806819³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21806849) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10903409 + 10903410.

It is an arithmetic number, because the mean of its divisors is an integer number (10903410).

Almost surely, 2^21806819 is an apocalyptic number.

21806819 is a deficient number, since it is larger than the sum of its proper divisors (1).

21806819 is an equidigital number, since it uses as much as digits as its factorization.

21806819 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6912, while the sum is 35.

The square root of 21806819 is about 4669.7771895456. Note that the first 3 decimals coincide. The cubic root of 21806819 is about 279.3813680448.

The spelling of 21806819 in words is "twenty-one million, eight hundred six thousand, eight hundred nineteen".