18513881 has 2 divisors, whose sum is σ = 18513882. Its totient is φ = 18513880.

The previous prime is 18513877. The next prime is 18513883. The reversal of 18513881 is 18831581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12138256 + 6375625 = 3484^2 + 2525^2 .

It is a cyclic number.

It is not a de Polignac number, because 18513881 - 2² = 18513877 is a prime.

It is a super-2 number, since 2×18513881² = 685527579364322, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 18513883, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (18513883) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9256940 + 9256941.

It is an arithmetic number, because the mean of its divisors is an integer number (9256941).

Almost surely, 2^18513881 is an apocalyptic number.

It is an amenable number.

18513881 is a deficient number, since it is larger than the sum of its proper divisors (1).

18513881 is an equidigital number, since it uses as much as digits as its factorization.

18513881 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7680, while the sum is 35.

The square root of 18513881 is about 4302.7759644211. The cubic root of 18513881 is about 264.5447553456.

The spelling of 18513881 in words is "eighteen million, five hundred thirteen thousand, eight hundred eighty-one".