20810781 has 12 divisors (see below), whose sum is σ = 30398940. Its totient is φ = 13717440.

The previous prime is 20810759. The next prime is 20810809. The reversal of 20810781 is 18701802.

It can be written as a sum of positive squares in 2 ways, for example, as 7371225 + 13439556 = 2715^2 + 3666^2 .

It is not a de Polignac number, because 20810781 - 2⁵ = 20810749 is a prime.

It is a super-2 number, since 2×20810781² = 866177211659922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20810731) 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 in 11 ways as a sum of consecutive naturals, for example, 12190 + ... + 13791.

It is an arithmetic number, because the mean of its divisors is an integer number (2533245).

Almost surely, 2^20810781 is an apocalyptic number.

It is an amenable number.

20810781 is a deficient number, since it is larger than the sum of its proper divisors (9588159).

20810781 is a wasteful number, since it uses less digits than its factorization.

20810781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26076 (or 26073 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 27.

The square root of 20810781 is about 4561.8834925938. The cubic root of 20810781 is about 275.0612800075.

The spelling of 20810781 in words is "twenty million, eight hundred ten thousand, seven hundred eighty-one".