21729289 has 2 divisors, whose sum is σ = 21729290. Its totient is φ = 21729288.

The previous prime is 21729269. The next prime is 21729307. The reversal of 21729289 is 98292712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21715600 + 13689 = 4660^2 + 117^2 .

It is a cyclic number.

It is not a de Polignac number, because 21729289 - 2⁷ = 21729161 is a prime.

It is not a weakly prime, because it can be changed into another prime (21729229) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10864644 + 10864645.

It is an arithmetic number, because the mean of its divisors is an integer number (10864645).

Almost surely, 2^21729289 is an apocalyptic number.

It is an amenable number.

21729289 is a deficient number, since it is larger than the sum of its proper divisors (1).

21729289 is an equidigital number, since it uses as much as digits as its factorization.

21729289 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 36288, while the sum is 40.

The square root of 21729289 is about 4661.4685454264. The cubic root of 21729289 is about 279.0498791018.

The spelling of 21729289 in words is "twenty-one million, seven hundred twenty-nine thousand, two hundred eighty-nine".