18481721 has 2 divisors, whose sum is σ = 18481722. Its totient is φ = 18481720.

The previous prime is 18481709. The next prime is 18481741. The reversal of 18481721 is 12718481.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13690000 + 4791721 = 3700^2 + 2189^2 .

It is a cyclic number.

It is not a de Polignac number, because 18481721 - 2²² = 14287417 is a prime.

It is a super-2 number, since 2×18481721² = 683148022243682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (18481741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9240860 + 9240861.

It is an arithmetic number, because the mean of its divisors is an integer number (9240861).

Almost surely, 2^18481721 is an apocalyptic number.

It is an amenable number.

18481721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18481721 is an equidigital number, since it uses as much as digits as its factorization.

18481721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3584, while the sum is 32.

The square root of 18481721 is about 4299.0372177966. The cubic root of 18481721 is about 264.3914885382.

The spelling of 18481721 in words is "eighteen million, four hundred eighty-one thousand, seven hundred twenty-one".