20561689 has 2 divisors, whose sum is σ = 20561690. Its totient is φ = 20561688.

The previous prime is 20561683. The next prime is 20561693. The reversal of 20561689 is 98616502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12250000 + 8311689 = 3500^2 + 2883^2 .

It is a cyclic number.

It is not a de Polignac number, because 20561689 - 2⁷ = 20561561 is a prime.

It is not a weakly prime, because it can be changed into another prime (20561683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10280844 + 10280845.

It is an arithmetic number, because the mean of its divisors is an integer number (10280845).

Almost surely, 2^20561689 is an apocalyptic number.

It is an amenable number.

20561689 is a deficient number, since it is larger than the sum of its proper divisors (1).

20561689 is an equidigital number, since it uses as much as digits as its factorization.

20561689 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 25920, while the sum is 37.

The square root of 20561689 is about 4534.4998621678. The cubic root of 20561689 is about 273.9594350945.

The spelling of 20561689 in words is "twenty million, five hundred sixty-one thousand, six hundred eighty-nine".