21302509 has 2 divisors, whose sum is σ = 21302510. Its totient is φ = 21302508.

The previous prime is 21302507. The next prime is 21302527. The reversal of 21302509 is 90520312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19669225 + 1633284 = 4435^2 + 1278^2 .

It is a cyclic number.

It is not a de Polignac number, because 21302509 - 2¹ = 21302507 is a prime.

Together with 21302507, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21302509.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21302507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10651254 + 10651255.

It is an arithmetic number, because the mean of its divisors is an integer number (10651255).

Almost surely, 2^21302509 is an apocalyptic number.

It is an amenable number.

21302509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21302509 is an equidigital number, since it uses as much as digits as its factorization.

21302509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 540, while the sum is 22.

The square root of 21302509 is about 4615.4641153409. The cubic root of 21302509 is about 277.2108678596.

The spelling of 21302509 in words is "twenty-one million, three hundred two thousand, five hundred nine".