21599729 has 2 divisors, whose sum is σ = 21599730. Its totient is φ = 21599728.

The previous prime is 21599719. The next prime is 21599791. The reversal of 21599729 is 92799512.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12285025 + 9314704 = 3505^2 + 3052^2 .

It is a cyclic number.

It is not a de Polignac number, because 21599729 - 2²⁴ = 4822513 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21599729.

It is not a weakly prime, because it can be changed into another prime (21599719) 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, 10799864 + 10799865.

It is an arithmetic number, because the mean of its divisors is an integer number (10799865).

Almost surely, 2^21599729 is an apocalyptic number.

It is an amenable number.

21599729 is a deficient number, since it is larger than the sum of its proper divisors (1).

21599729 is an equidigital number, since it uses as much as digits as its factorization.

21599729 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 102060, while the sum is 44.

The square root of 21599729 is about 4647.5508603995. The cubic root of 21599729 is about 278.4941653169.

The spelling of 21599729 in words is "twenty-one million, five hundred ninety-nine thousand, seven hundred twenty-nine".