18515881 has 2 divisors, whose sum is σ = 18515882. Its totient is φ = 18515880.

The previous prime is 18515869. The next prime is 18515951. The reversal of 18515881 is 18851581.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17505856 + 1010025 = 4184^2 + 1005^2 .

It is a cyclic number.

It is not a de Polignac number, because 18515881 - 2⁷ = 18515753 is a prime.

It is a super-2 number, since 2×18515881² = 685675698412322, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 18515881.

It is not a weakly prime, because it can be changed into another prime (18515801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9257940 + 9257941.

It is an arithmetic number, because the mean of its divisors is an integer number (9257941).

Almost surely, 2^18515881 is an apocalyptic number.

It is an amenable number.

18515881 is a deficient number, since it is larger than the sum of its proper divisors (1).

18515881 is an equidigital number, since it uses as much as digits as its factorization.

18515881 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12800, while the sum is 37.

The square root of 18515881 is about 4303.0083662480. The cubic root of 18515881 is about 264.5542809993.

The spelling of 18515881 in words is "eighteen million, five hundred fifteen thousand, eight hundred eighty-one".