18910981 has 2 divisors, whose sum is σ = 18910982. Its totient is φ = 18910980.

The previous prime is 18910943. The next prime is 18910993. The reversal of 18910981 is 18901981.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17892900 + 1018081 = 4230^2 + 1009^2 .

It is a cyclic number.

It is not a de Polignac number, because 18910981 - 2⁹ = 18910469 is a prime.

It is a super-2 number, since 2×18910981² = 715250404764722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 18910981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18910901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9455490 + 9455491.

It is an arithmetic number, because the mean of its divisors is an integer number (9455491).

Almost surely, 2^18910981 is an apocalyptic number.

It is an amenable number.

18910981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18910981 is an equidigital number, since it uses as much as digits as its factorization.

18910981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5184, while the sum is 37.

The square root of 18910981 is about 4348.6757754516. The cubic root of 18910981 is about 266.4227782274.

It can be divided in two parts, 18910 and 981, that added together give a palindrome (19891).

The spelling of 18910981 in words is "eighteen million, nine hundred ten thousand, nine hundred eighty-one".