20905645 has 4 divisors (see below), whose sum is σ = 25086780. Its totient is φ = 16724512.

The previous prime is 20905637. The next prime is 20905657. The reversal of 20905645 is 54650902.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 54650902 = 2 ⋅27325451.

It can be written as a sum of positive squares in 2 ways, for example, as 4405801 + 16499844 = 2099^2 + 4062^2 .

It is a cyclic number.

It is not a de Polignac number, because 20905645 - 2³ = 20905637 is a prime.

It is a super-3 number, since 3×20905645³ (a number of 23 digits) contains 333 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2090560 + ... + 2090569.

It is an arithmetic number, because the mean of its divisors is an integer number (6271695).

Almost surely, 2^20905645 is an apocalyptic number.

It is an amenable number.

20905645 is a deficient number, since it is larger than the sum of its proper divisors (4181135).

20905645 is an equidigital number, since it uses as much as digits as its factorization.

20905645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4181134.

The product of its (nonzero) digits is 10800, while the sum is 31.

The square root of 20905645 is about 4572.2691303116. The cubic root of 20905645 is about 275.4785935983.

The spelling of 20905645 in words is "twenty million, nine hundred five thousand, six hundred forty-five".