9918721 has 2 divisors, whose sum is σ = 9918722. Its totient is φ = 9918720.

The previous prime is 9918709. The next prime is 9918743. The reversal of 9918721 is 1278199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 6350400 + 3568321 = 2520^2 + 1889^2 .

It is a cyclic number.

It is not a de Polignac number, because 9918721 - 2⁷ = 9918593 is a prime.

It is not a weakly prime, because it can be changed into another prime (9918121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4959360 + 4959361.

It is an arithmetic number, because the mean of its divisors is an integer number (4959361).

Almost surely, 2^9918721 is an apocalyptic number.

It is an amenable number.

9918721 is a deficient number, since it is larger than the sum of its proper divisors (1).

9918721 is an equidigital number, since it uses as much as digits as its factorization.

9918721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9072, while the sum is 37.

The square root of 9918721 is about 3149.4001016067. The cubic root of 9918721 is about 214.8581794117.

The spelling of 9918721 in words is "nine million, nine hundred eighteen thousand, seven hundred twenty-one".