18447721 has 2 divisors, whose sum is σ = 18447722. Its totient is φ = 18447720.

The previous prime is 18447691. The next prime is 18447739. The reversal of 18447721 is 12774481.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18156121 + 291600 = 4261^2 + 540^2 .

It is a cyclic number.

It is not a de Polignac number, because 18447721 - 2⁷ = 18447593 is a prime.

It is not a weakly prime, because it can be changed into another prime (18447421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9223860 + 9223861.

It is an arithmetic number, because the mean of its divisors is an integer number (9223861).

Almost surely, 2^18447721 is an apocalyptic number.

It is an amenable number.

18447721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18447721 is an equidigital number, since it uses as much as digits as its factorization.

18447721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12544, while the sum is 34.

The square root of 18447721 is about 4295.0810236828. The cubic root of 18447721 is about 264.2292592620.

The spelling of 18447721 in words is "eighteen million, four hundred forty-seven thousand, seven hundred twenty-one".