18751981 has 2 divisors, whose sum is σ = 18751982. Its totient is φ = 18751980.

The previous prime is 18751979. The next prime is 18751991. The reversal of 18751981 is 18915781.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13205956 + 5546025 = 3634^2 + 2355^2 .

It is a cyclic number.

It is not a de Polignac number, because 18751981 - 2¹ = 18751979 is a prime.

It is a super-2 number, since 2×18751981² = 703273582848722, which contains 22 as substring.

Together with 18751979, it forms a pair of twin primes.

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 pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9375990 + 9375991.

It is an arithmetic number, because the mean of its divisors is an integer number (9375991).

Almost surely, 2^18751981 is an apocalyptic number.

It is an amenable number.

18751981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18751981 is an equidigital number, since it uses as much as digits as its factorization.

18751981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20160, while the sum is 40.

The square root of 18751981 is about 4330.3557590572. The cubic root of 18751981 is about 265.6739980845.

The spelling of 18751981 in words is "eighteen million, seven hundred fifty-one thousand, nine hundred eighty-one".