399640987 has 2 divisors, whose sum is σ = 399640988. Its totient is φ = 399640986.

The previous prime is 399640973. The next prime is 399640993. The reversal of 399640987 is 789046993.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 399640987 - 2¹⁵ = 399608219 is a prime.

It is not a weakly prime, because it can be changed into another prime (399640907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 199820493 + 199820494.

It is an arithmetic number, because the mean of its divisors is an integer number (199820494).

Almost surely, 2^399640987 is an apocalyptic number.

399640987 is a deficient number, since it is larger than the sum of its proper divisors (1).

399640987 is an equidigital number, since it uses as much as digits as its factorization.

399640987 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2939328, while the sum is 55.

The square root of 399640987 is about 19991.0226601842. The cubic root of 399640987 is about 736.5857978790.

The spelling of 399640987 in words is "three hundred ninety-nine million, six hundred forty thousand, nine hundred eighty-seven".