18687391 has 2 divisors, whose sum is σ = 18687392. Its totient is φ = 18687390.

The previous prime is 18687379. The next prime is 18687401. The reversal of 18687391 is 19378681.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 18687391 - 2¹⁷ = 18556319 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18687311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9343695 + 9343696.

It is an arithmetic number, because the mean of its divisors is an integer number (9343696).

Almost surely, 2^18687391 is an apocalyptic number.

18687391 is a deficient number, since it is larger than the sum of its proper divisors (1).

18687391 is an equidigital number, since it uses as much as digits as its factorization.

18687391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72576, while the sum is 43.

The square root of 18687391 is about 4322.8915091637. The cubic root of 18687391 is about 265.3686148228.

The spelling of 18687391 in words is "eighteen million, six hundred eighty-seven thousand, three hundred ninety-one".