209918979393561 has 27 divisors (see below), whose sum is σ = 305098235983359. Its totient is φ = 139082727629232.

The previous prime is 209918979393559. The next prime is 209918979393583. The reversal of 209918979393561 is 165393979819902.

The square root of 209918979393561 is 14488581.

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

209918979393561 is a `hidden beast` number, since 2 + 0 + 9 + 9 + 18 + 9 + 7 + 9 + 39 + 3 + 561 = 666.

209918979393561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 189767678833161 + 20151300560400 = 13775619^2 + 4489020^2 .

It is not a de Polignac number, because 209918979393561 - 2¹ = 209918979393559 is a prime.

It is not an unprimeable number, because it can be changed into a prime (209918979393511) 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, 7084901295 + ... + 7084930923.

Almost surely, 2^{209918979393561} is an apocalyptic number.

209918979393561 is the 14488581-st square number.

209918979393561 is the 7244291-st centered octagonal number.

It is an amenable number.

209918979393561 is a deficient number, since it is larger than the sum of its proper divisors (95179256589798).

209918979393561 is an frugal number, since it uses more digits than its factorization.

209918979393561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59590 (or 29795 counting only the distinct ones).

The product of its (nonzero) digits is 1785641760, while the sum is 81.

The spelling of 209918979393561 in words is "two hundred nine trillion, nine hundred eighteen billion, nine hundred seventy-nine million, three hundred ninety-three thousand, five hundred sixty-one".