21808933 has 2 divisors, whose sum is σ = 21808934. Its totient is φ = 21808932.

The previous prime is 21808921. The next prime is 21808939. The reversal of 21808933 is 33980812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14152644 + 7656289 = 3762^2 + 2767^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21808933 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21808939) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904466 + 10904467.

It is an arithmetic number, because the mean of its divisors is an integer number (10904467).

Almost surely, 2^21808933 is an apocalyptic number.

It is an amenable number.

21808933 is a deficient number, since it is larger than the sum of its proper divisors (1).

21808933 is an equidigital number, since it uses as much as digits as its factorization.

21808933 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10368, while the sum is 34.

The square root of 21808933 is about 4670.0035331892. The cubic root of 21808933 is about 279.3903956969.

The spelling of 21808933 in words is "twenty-one million, eight hundred eight thousand, nine hundred thirty-three".