20389981 has 4 divisors (see below), whose sum is σ = 20591964. Its totient is φ = 20188000.

The previous prime is 20389951. The next prime is 20389991. The reversal of 20389981 is 18998302.

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 18567481 + 1822500 = 4309^2 + 1350^2 .

It is a cyclic number.

It is not a de Polignac number, because 20389981 - 2¹³ = 20381789 is a prime.

It is a super-2 number, since 2×20389981² = 831502650360722, 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 (20389951) 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, 100840 + ... + 101041.

It is an arithmetic number, because the mean of its divisors is an integer number (5147991).

Almost surely, 2^20389981 is an apocalyptic number.

It is an amenable number.

20389981 is a deficient number, since it is larger than the sum of its proper divisors (201983).

20389981 is a wasteful number, since it uses less digits than its factorization.

20389981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201982.

The product of its (nonzero) digits is 31104, while the sum is 40.

The square root of 20389981 is about 4515.5266580987. The cubic root of 20389981 is about 273.1947024876.

The spelling of 20389981 in words is "twenty million, three hundred eighty-nine thousand, nine hundred eighty-one".