398787721 has 2 divisors, whose sum is σ = 398787722. Its totient is φ = 398787720.

The previous prime is 398787709. The next prime is 398787743. The reversal of 398787721 is 127787893.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 387302400 + 11485321 = 19680^2 + 3389^2 .

It is an emirp because it is prime and its reverse (127787893) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 398787721 - 2⁹ = 398787209 is a prime.

It is not a weakly prime, because it can be changed into another prime (398787421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 199393860 + 199393861.

It is an arithmetic number, because the mean of its divisors is an integer number (199393861).

Almost surely, 2^398787721 is an apocalyptic number.

It is an amenable number.

398787721 is a deficient number, since it is larger than the sum of its proper divisors (1).

398787721 is an equidigital number, since it uses as much as digits as its factorization.

398787721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1185408, while the sum is 52.

The square root of 398787721 is about 19969.6700273189. The cubic root of 398787721 is about 736.0612008270.

The spelling of 398787721 in words is "three hundred ninety-eight million, seven hundred eighty-seven thousand, seven hundred twenty-one".