18688981 has 2 divisors, whose sum is σ = 18688982. Its totient is φ = 18688980.

The previous prime is 18688979. The next prime is 18688991. The reversal of 18688981 is 18988681.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10080625 + 8608356 = 3175^2 + 2934^2 .

It is a cyclic number.

It is not a de Polignac number, because 18688981 - 2¹ = 18688979 is a prime.

It is a super-2 number, since 2×18688981² = 698556021636722, which contains 22 as substring.

Together with 18688979, it forms a pair of twin primes.

It is a Chen prime.

18688981 is a strobogrammatic number because it is the same when read upside-down.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18688931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9344490 + 9344491.

It is an arithmetic number, because the mean of its divisors is an integer number (9344491).

Almost surely, 2^18688981 is an apocalyptic number.

It is an amenable number.

18688981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18688981 is an equidigital number, since it uses as much as digits as its factorization.

18688981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 221184, while the sum is 49.

The square root of 18688981 is about 4323.0754099368. The cubic root of 18688981 is about 265.3761408267.

The spelling of 18688981 in words is "eighteen million, six hundred eighty-eight thousand, nine hundred eighty-one".