21016609 has 2 divisors, whose sum is σ = 21016610. Its totient is φ = 21016608.

The previous prime is 21016601. The next prime is 21016613. The reversal of 21016609 is 90661012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20277009 + 739600 = 4503^2 + 860^2 .

It is a cyclic number.

It is not a de Polignac number, because 21016609 - 2³ = 21016601 is a prime.

It is not a weakly prime, because it can be changed into another prime (21016601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10508304 + 10508305.

It is an arithmetic number, because the mean of its divisors is an integer number (10508305).

Almost surely, 2^21016609 is an apocalyptic number.

It is an amenable number.

21016609 is a deficient number, since it is larger than the sum of its proper divisors (1).

21016609 is an equidigital number, since it uses as much as digits as its factorization.

21016609 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 25.

The square root of 21016609 is about 4584.3875272494. The cubic root of 21016609 is about 275.9651333467.

The spelling of 21016609 in words is "twenty-one million, sixteen thousand, six hundred nine".