18987817 has 4 divisors (see below), whose sum is σ = 19124560. Its totient is φ = 18851076.

The previous prime is 18987803. The next prime is 18987853. The reversal of 18987817 is 71878981.

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: 71878981 = 89 ⋅807629.

It is a cyclic number.

It is not a de Polignac number, because 18987817 - 2²³ = 10599209 is a prime.

It is a super-3 number, since 3×18987817³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18987877) 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, 68163 + ... + 68440.

It is an arithmetic number, because the mean of its divisors is an integer number (4781140).

Almost surely, 2^18987817 is an apocalyptic number.

It is an amenable number.

18987817 is a deficient number, since it is larger than the sum of its proper divisors (136743).

18987817 is a wasteful number, since it uses less digits than its factorization.

18987817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 136742.

The product of its digits is 225792, while the sum is 49.

The square root of 18987817 is about 4357.5012335053. The cubic root of 18987817 is about 266.7831191035.

The spelling of 18987817 in words is "eighteen million, nine hundred eighty-seven thousand, eight hundred seventeen".