405209906721 has 15 divisors (see below), whose sum is σ = 605322122691. Its totient is φ = 270136118448.

The previous prime is 405209906693. The next prime is 405209906723. The reversal of 405209906721 is 127609902504.

The square root of 405209906721 is 636561.

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

405209906721 is a `hidden beast` number, since 40 + 520 + 9 + 9 + 0 + 67 + 21 = 666.

It can be written as a sum of positive squares in only one way, i.e., 256553393121 + 148656513600 = 506511^2 + 385560^2 .

It is not a de Polignac number, because 405209906721 - 2¹⁵ = 405209873953 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (405209906723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 5693685 + ... + 5764413.

Almost surely, 2^405209906721 is an apocalyptic number.

405209906721 is the 636561-st square number.

405209906721 is the 318281-st centered octagonal number.

It is an amenable number.

405209906721 is a deficient number, since it is larger than the sum of its proper divisors (200112215970).

405209906721 is an frugal number, since it uses more digits than its factorization.

405209906721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 141470 (or 70732 counting only the distinct ones).

The product of its (nonzero) digits is 272160, while the sum is 45.

The spelling of 405209906721 in words is "four hundred five billion, two hundred nine million, nine hundred six thousand, seven hundred twenty-one".