18421981 has 4 divisors (see below), whose sum is σ = 18591100. Its totient is φ = 18252864.

The previous prime is 18421973. The next prime is 18421987. The reversal of 18421981 is 18912481.

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 10208025 + 8213956 = 3195^2 + 2866^2 .

It is a cyclic number.

It is not a de Polignac number, because 18421981 - 2³ = 18421973 is a prime.

It is a super-2 number, since 2×18421981² = 678738767928722, 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 (18421987) 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, 84396 + ... + 84613.

It is an arithmetic number, because the mean of its divisors is an integer number (4647775).

Almost surely, 2^18421981 is an apocalyptic number.

It is an amenable number.

18421981 is a deficient number, since it is larger than the sum of its proper divisors (169119).

18421981 is a wasteful number, since it uses less digits than its factorization.

18421981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 169118.

The product of its digits is 4608, while the sum is 34.

The square root of 18421981 is about 4292.0835266803. The cubic root of 18421981 is about 264.1063095340.

It can be divided in two parts, 18421 and 981, that multiplied together give a square (18071001 = 4251²).

The spelling of 18421981 in words is "eighteen million, four hundred twenty-one thousand, nine hundred eighty-one".