20643881 has 4 divisors (see below), whose sum is σ = 20695764. Its totient is φ = 20592000.

The previous prime is 20643851. The next prime is 20643893. The reversal of 20643881 is 18834602.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14318656 + 6325225 = 3784^2 + 2515^2 .

It is a cyclic number.

It is not a de Polignac number, because 20643881 - 2¹⁰ = 20642857 is a prime.

It is a super-2 number, since 2×20643881² = 852339645484322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20643851) 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, 25340 + ... + 26141.

It is an arithmetic number, because the mean of its divisors is an integer number (5173941).

Almost surely, 2^20643881 is an apocalyptic number.

It is an amenable number.

20643881 is a deficient number, since it is larger than the sum of its proper divisors (51883).

20643881 is an equidigital number, since it uses as much as digits as its factorization.

20643881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51882.

The product of its (nonzero) digits is 9216, while the sum is 32.

The square root of 20643881 is about 4543.5537853095. The cubic root of 20643881 is about 274.3239858422.

The spelling of 20643881 in words is "twenty million, six hundred forty-three thousand, eight hundred eighty-one".