21252809 has 2 divisors, whose sum is σ = 21252810. Its totient is φ = 21252808.

The previous prime is 21252799. The next prime is 21252821. The reversal of 21252809 is 90825212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20675209 + 577600 = 4547^2 + 760^2 .

It is a cyclic number.

It is not a de Polignac number, because 21252809 - 2¹² = 21248713 is a prime.

It is a super-3 number, since 3×21252809³ (a number of 23 digits) contains 333 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21252899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10626404 + 10626405.

It is an arithmetic number, because the mean of its divisors is an integer number (10626405).

Almost surely, 2^21252809 is an apocalyptic number.

It is an amenable number.

21252809 is a deficient number, since it is larger than the sum of its proper divisors (1).

21252809 is an equidigital number, since it uses as much as digits as its factorization.

21252809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 21252809 is about 4610.0768974064. The cubic root of 21252809 is about 276.9951169275.

The spelling of 21252809 in words is "twenty-one million, two hundred fifty-two thousand, eight hundred nine".