18751991 has 2 divisors, whose sum is σ = 18751992. Its totient is φ = 18751990.

The previous prime is 18751981. The next prime is 18752039. The reversal of 18751991 is 19915781.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 18751991 - 2⁶ = 18751927 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18751961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9375995 + 9375996.

It is an arithmetic number, because the mean of its divisors is an integer number (9375996).

Almost surely, 2^18751991 is an apocalyptic number.

18751991 is a deficient number, since it is larger than the sum of its proper divisors (1).

18751991 is an equidigital number, since it uses as much as digits as its factorization.

18751991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 22680, while the sum is 41.

The square root of 18751991 is about 4330.3569136966. The cubic root of 18751991 is about 265.6740453104.

The spelling of 18751991 in words is "eighteen million, seven hundred fifty-one thousand, nine hundred ninety-one".