20505689 has 8 divisors (see below), whose sum is σ = 21957480. Its totient is φ = 19081216.

The previous prime is 20505679. The next prime is 20505691. The reversal of 20505689 is 98650502.

20505689 = 247² + 248² + ... + 424².

It can be written as a sum of positive squares in 4 ways, for example, as 5139289 + 15366400 = 2267^2 + 3920^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20505689 - 2¹⁶ = 20440153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20505619) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5264 + ... + 8289.

It is an arithmetic number, because the mean of its divisors is an integer number (2744685).

Almost surely, 2^20505689 is an apocalyptic number.

It is an amenable number.

20505689 is a deficient number, since it is larger than the sum of its proper divisors (1451791).

20505689 is a wasteful number, since it uses less digits than its factorization.

20505689 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13659.

The product of its (nonzero) digits is 21600, while the sum is 35.

The square root of 20505689 is about 4528.3207704402. The cubic root of 20505689 is about 273.7104983904.

It can be divided in two parts, 205056 and 89, that multiplied together give a square (18249984 = 4272²).

The spelling of 20505689 in words is "twenty million, five hundred five thousand, six hundred eighty-nine".