20051981 has 4 divisors (see below), whose sum is σ = 20380764. Its totient is φ = 19723200.

The previous prime is 20051971. The next prime is 20051987. The reversal of 20051981 is 18915002.

It is a happy number.

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 3118756 + 16933225 = 1766^2 + 4115^2 .

It is a cyclic number.

It is not a de Polignac number, because 20051981 - 2¹⁰ = 20050957 is a prime.

It is a super-2 number, since 2×20051981² = 804163884048722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20051981.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20051987) 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, 164300 + ... + 164421.

It is an arithmetic number, because the mean of its divisors is an integer number (5095191).

Almost surely, 2^20051981 is an apocalyptic number.

It is an amenable number.

20051981 is a deficient number, since it is larger than the sum of its proper divisors (328783).

20051981 is an equidigital number, since it uses as much as digits as its factorization.

20051981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 328782.

The product of its (nonzero) digits is 720, while the sum is 26.

The square root of 20051981 is about 4477.9438361820. The cubic root of 20051981 is about 271.6767217894.

Adding to 20051981 its reverse (18915002), we get a palindrome (38966983).

The spelling of 20051981 in words is "twenty million, fifty-one thousand, nine hundred eighty-one".