399185139721 has 27 divisors (see below), whose sum is σ = 418993749333. Its totient is φ = 380299677120.

The previous prime is 399185139713. The next prime is 399185139767. The reversal of 399185139721 is 127931581993.

The square root of 399185139721 is 631811.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 14015955321 + 385169184400 = 118389^2 + 620620^2 .

It is not a de Polignac number, because 399185139721 - 2³ = 399185139713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (399185139701) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 1743166435 + ... + 1743166663.

Almost surely, 2^399185139721 is an apocalyptic number.

399185139721 is a gapful number since it is divisible by the number (31) formed by its first and last digit.

399185139721 is the 631811-st square number.

399185139721 is the 315906-th centered octagonal number.

It is an amenable number.

399185139721 is a deficient number, since it is larger than the sum of its proper divisors (19808609612).

399185139721 is an frugal number, since it uses more digits than its factorization.

399185139721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 698 (or 349 counting only the distinct ones).

The product of its digits is 3674160, while the sum is 58.

The spelling of 399185139721 in words is "three hundred ninety-nine billion, one hundred eighty-five million, one hundred thirty-nine thousand, seven hundred twenty-one".