18613981 has 4 divisors (see below), whose sum is σ = 19214464. Its totient is φ = 18013500.

The previous prime is 18613979. The next prime is 18614003. The reversal of 18613981 is 18931681.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18931681 = 113 ⋅167537.

It is a cyclic number.

It is not a de Polignac number, because 18613981 - 2¹ = 18613979 is a prime.

It is a super-2 number, since 2×18613981² = 692960577336722, 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 18613981.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18613481) 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, 300195 + ... + 300256.

It is an arithmetic number, because the mean of its divisors is an integer number (4803616).

Almost surely, 2^18613981 is an apocalyptic number.

It is an amenable number.

18613981 is a deficient number, since it is larger than the sum of its proper divisors (600483).

18613981 is an equidigital number, since it uses as much as digits as its factorization.

18613981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 600482.

The product of its digits is 10368, while the sum is 37.

The square root of 18613981 is about 4314.3923094684. The cubic root of 18613981 is about 265.0206747842.

The spelling of 18613981 in words is "eighteen million, six hundred thirteen thousand, nine hundred eighty-one".