20865581 has 4 divisors (see below), whose sum is σ = 22762464. Its totient is φ = 18968700.

The previous prime is 20865557. The next prime is 20865583. The reversal of 20865581 is 18556802.

It is a happy number.

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.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20865581 is a prime.

It is a super-2 number, since 2×20865581² = 870744940935122, 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 (20865583) 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, 948425 + ... + 948446.

It is an arithmetic number, because the mean of its divisors is an integer number (5690616).

Almost surely, 2^20865581 is an apocalyptic number.

It is an amenable number.

20865581 is a deficient number, since it is larger than the sum of its proper divisors (1896883).

20865581 is a wasteful number, since it uses less digits than its factorization.

20865581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1896882.

The product of its (nonzero) digits is 19200, while the sum is 35.

The square root of 20865581 is about 4567.8858348256. The cubic root of 20865581 is about 275.3025034840.

It can be divided in two parts, 2086 and 5581, that added together give a palindrome (7667).

The spelling of 20865581 in words is "twenty million, eight hundred sixty-five thousand, five hundred eighty-one".