18406981 has 2 divisors, whose sum is σ = 18406982. Its totient is φ = 18406980.

The previous prime is 18406979. The next prime is 18406987. The reversal of 18406981 is 18960481.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17388900 + 1018081 = 4170^2 + 1009^2 .

It is an emirp because it is prime and its reverse (18960481) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18406981 - 2¹ = 18406979 is a prime.

It is a super-2 number, since 2×18406981² = 677633899068722, which contains 22 as substring.

Together with 18406979, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 18406981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18406987) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9203490 + 9203491.

It is an arithmetic number, because the mean of its divisors is an integer number (9203491).

Almost surely, 2^18406981 is an apocalyptic number.

It is an amenable number.

18406981 is a deficient number, since it is larger than the sum of its proper divisors (1).

18406981 is an equidigital number, since it uses as much as digits as its factorization.

18406981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 13824, while the sum is 37.

The square root of 18406981 is about 4290.3357677459. The cubic root of 18406981 is about 264.0346076838.

The spelling of 18406981 in words is "eighteen million, four hundred six thousand, nine hundred eighty-one".