20811661 has 4 divisors (see below), whose sum is σ = 22412572. Its totient is φ = 19210752.

The previous prime is 20811653. The next prime is 20811667. The reversal of 20811661 is 16611802.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16611802 = 2 ⋅8305901.

It can be written as a sum of positive squares in 2 ways, for example, as 10692900 + 10118761 = 3270^2 + 3181^2 .

It is a cyclic number.

It is not a de Polignac number, because 20811661 - 2³ = 20811653 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20811667) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 800436 + ... + 800461.

It is an arithmetic number, because the mean of its divisors is an integer number (5603143).

Almost surely, 2^20811661 is an apocalyptic number.

It is an amenable number.

20811661 is a deficient number, since it is larger than the sum of its proper divisors (1600911).

20811661 is a wasteful number, since it uses less digits than its factorization.

20811661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1600910.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 20811661 is about 4561.9799429634. The cubic root of 20811661 is about 275.0651570126.

The spelling of 20811661 in words is "twenty million, eight hundred eleven thousand, six hundred sixty-one".