21720833 has 2 divisors, whose sum is σ = 21720834. Its totient is φ = 21720832.

The previous prime is 21720827. The next prime is 21720877. The reversal of 21720833 is 33802712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14500864 + 7219969 = 3808^2 + 2687^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21720833 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21720233) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860416 + 10860417.

It is an arithmetic number, because the mean of its divisors is an integer number (10860417).

Almost surely, 2^21720833 is an apocalyptic number.

It is an amenable number.

21720833 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720833 is an equidigital number, since it uses as much as digits as its factorization.

21720833 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2016, while the sum is 26.

The square root of 21720833 is about 4660.5614468645. The cubic root of 21720833 is about 279.0136767832.

The spelling of 21720833 in words is "twenty-one million, seven hundred twenty thousand, eight hundred thirty-three".