399721561 has 8 divisors (see below), whose sum is σ = 425086920. Its totient is φ = 374562048.

The previous prime is 399721559. The next prime is 399721583. The reversal of 399721561 is 165127993.

It can be written as a sum of positive squares in 4 ways, for example, as 162715536 + 237006025 = 12756^2 + 15395^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 399721561 - 2¹ = 399721559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (399721541) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 47446 + ... + 55231.

It is an arithmetic number, because the mean of its divisors is an integer number (53135865).

Almost surely, 2^399721561 is an apocalyptic number.

It is an amenable number.

399721561 is a deficient number, since it is larger than the sum of its proper divisors (25365359).

399721561 is a wasteful number, since it uses less digits than its factorization.

399721561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 102923.

The product of its digits is 102060, while the sum is 43.

The square root of 399721561 is about 19993.0378131989. The cubic root of 399721561 is about 736.6352970360.

The spelling of 399721561 in words is "three hundred ninety-nine million, seven hundred twenty-one thousand, five hundred sixty-one".