18531881 has 2 divisors, whose sum is σ = 18531882. Its totient is φ = 18531880.

The previous prime is 18531829. The next prime is 18531883. The reversal of 18531881 is 18813581.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16736281 + 1795600 = 4091^2 + 1340^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18531881 is a prime.

It is a super-2 number, since 2×18531881² = 686861226796322, which contains 22 as substring.

Together with 18531883, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18531883) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9265940 + 9265941.

It is an arithmetic number, because the mean of its divisors is an integer number (9265941).

Almost surely, 2^18531881 is an apocalyptic number.

It is an amenable number.

18531881 is a deficient number, since it is larger than the sum of its proper divisors (1).

18531881 is an equidigital number, since it uses as much as digits as its factorization.

18531881 is an odious number, because the sum of its binary digits is odd.

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

The square root of 18531881 is about 4304.8671291923. The cubic root of 18531881 is about 264.6304615466.

It can be divided in two parts, 185 and 31881, that multiplied together give a palindrome (5897985).

The spelling of 18531881 in words is "eighteen million, five hundred thirty-one thousand, eight hundred eighty-one".