20491609 has 2 divisors, whose sum is σ = 20491610. Its totient is φ = 20491608.

The previous prime is 20491591. The next prime is 20491631. The reversal of 20491609 is 90619402.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14040009 + 6451600 = 3747^2 + 2540^2 .

It is a cyclic number.

It is not a de Polignac number, because 20491609 - 2¹¹ = 20489561 is a prime.

It is not a weakly prime, because it can be changed into another prime (20491699) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10245804 + 10245805.

It is an arithmetic number, because the mean of its divisors is an integer number (10245805).

Almost surely, 2^20491609 is an apocalyptic number.

It is an amenable number.

20491609 is a deficient number, since it is larger than the sum of its proper divisors (1).

20491609 is an equidigital number, since it uses as much as digits as its factorization.

20491609 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 20491609 is about 4526.7658432925. The cubic root of 20491609 is about 273.6478373045.

The spelling of 20491609 in words is "twenty million, four hundred ninety-one thousand, six hundred nine".