21361609 has 2 divisors, whose sum is σ = 21361610. Its totient is φ = 21361608.

The previous prime is 21361591. The next prime is 21361619. The reversal of 21361609 is 90616312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18020025 + 3341584 = 4245^2 + 1828^2 .

It is a cyclic number.

It is not a de Polignac number, because 21361609 - 2⁹ = 21361097 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21361619) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10680804 + 10680805.

It is an arithmetic number, because the mean of its divisors is an integer number (10680805).

Almost surely, 2^21361609 is an apocalyptic number.

It is an amenable number.

21361609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21361609 is an equidigital number, since it uses as much as digits as its factorization.

21361609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 21361609 is about 4621.8620706378. The cubic root of 21361609 is about 277.4669884709.

The spelling of 21361609 in words is "twenty-one million, three hundred sixty-one thousand, six hundred nine".