18521381 has 8 divisors (see below), whose sum is σ = 20089944. Its totient is φ = 17006080.

The previous prime is 18521329. The next prime is 18521407. The reversal of 18521381 is 18312581.

It can be written as a sum of positive squares in 4 ways, for example, as 6584356 + 11937025 = 2566^2 + 3455^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 18521381 - 2⁶ = 18521317 is a prime.

It is a super-2 number, since 2×18521381² = 686083108294322, 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 (18521311) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12590 + ... + 13983.

It is an arithmetic number, because the mean of its divisors is an integer number (2511243).

Almost surely, 2^18521381 is an apocalyptic number.

It is an amenable number.

18521381 is a deficient number, since it is larger than the sum of its proper divisors (1568563).

18521381 is a wasteful number, since it uses less digits than its factorization.

18521381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26631.

The product of its digits is 1920, while the sum is 29.

The square root of 18521381 is about 4303.6474065611. The cubic root of 18521381 is about 264.5804730107.

The spelling of 18521381 in words is "eighteen million, five hundred twenty-one thousand, three hundred eighty-one".