20516581 has 4 divisors (see below), whose sum is σ = 20953152. Its totient is φ = 20080012.

The previous prime is 20516549. The next prime is 20516591. The reversal of 20516581 is 18561502.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18561502 = 2 ⋅9280751.

It is a cyclic number.

It is not a de Polignac number, because 20516581 - 2⁵ = 20516549 is a prime.

It is a super-2 number, since 2×20516581² = 841860191859122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20516591) 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 3 ways as a sum of consecutive naturals, for example, 218215 + ... + 218308.

It is an arithmetic number, because the mean of its divisors is an integer number (5238288).

Almost surely, 2^20516581 is an apocalyptic number.

It is an amenable number.

20516581 is a deficient number, since it is larger than the sum of its proper divisors (436571).

20516581 is an equidigital number, since it uses as much as digits as its factorization.

20516581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 436570.

The product of its (nonzero) digits is 2400, while the sum is 28.

The square root of 20516581 is about 4529.5232640974. The cubic root of 20516581 is about 273.7589520505.

The spelling of 20516581 in words is "twenty million, five hundred sixteen thousand, five hundred eighty-one".