18957721 has 2 divisors, whose sum is σ = 18957722. Its totient is φ = 18957720.

The previous prime is 18957707. The next prime is 18957733. The reversal of 18957721 is 12775981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16281225 + 2676496 = 4035^2 + 1636^2 .

It is an emirp because it is prime and its reverse (12775981) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18957721 - 2⁵ = 18957689 is a prime.

It is not a weakly prime, because it can be changed into another prime (18957761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9478860 + 9478861.

It is an arithmetic number, because the mean of its divisors is an integer number (9478861).

Almost surely, 2^18957721 is an apocalyptic number.

It is an amenable number.

18957721 is a deficient number, since it is larger than the sum of its proper divisors (1).

18957721 is an equidigital number, since it uses as much as digits as its factorization.

18957721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 35280, while the sum is 40.

The square root of 18957721 is about 4354.0465087089. The cubic root of 18957721 is about 266.6420927008.

The spelling of 18957721 in words is "eighteen million, nine hundred fifty-seven thousand, seven hundred twenty-one".