21221509 has 2 divisors, whose sum is σ = 21221510. Its totient is φ = 21221508.

The previous prime is 21221503. The next prime is 21221521. The reversal of 21221509 is 90512212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14861025 + 6360484 = 3855^2 + 2522^2 .

It is a cyclic number.

It is not a de Polignac number, because 21221509 - 2⁷ = 21221381 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21221509.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21221503) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610754 + 10610755.

It is an arithmetic number, because the mean of its divisors is an integer number (10610755).

Almost surely, 2^21221509 is an apocalyptic number.

It is an amenable number.

21221509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221509 is an equidigital number, since it uses as much as digits as its factorization.

21221509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21221509 is about 4606.6809092882. The cubic root of 21221509 is about 276.8590689215.

The spelling of 21221509 in words is "twenty-one million, two hundred twenty-one thousand, five hundred nine".