211755508561 has 9 divisors (see below), whose sum is σ = 217650809649. Its totient is φ = 206015820624.

The previous prime is 211755508429. The next prime is 211755508577. The reversal of 211755508561 is 165805557112.

The square root of 211755508561 is 460169.

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 4111246161 + 207644262400 = 64119^2 + 455680^2 .

It is not a de Polignac number, because 211755508561 - 2¹¹ = 211755506513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (211755508661) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 17020035 + ... + 17032471.

Almost surely, 2^211755508561 is an apocalyptic number.

211755508561 is the 460169-th square number.

211755508561 is the 230085-th centered octagonal number.

It is an amenable number.

211755508561 is a deficient number, since it is larger than the sum of its proper divisors (5895301088).

211755508561 is an frugal number, since it uses more digits than its factorization.

211755508561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24948 (or 12474 counting only the distinct ones).

The product of its (nonzero) digits is 420000, while the sum is 46.

The spelling of 211755508561 in words is "two hundred eleven billion, seven hundred fifty-five million, five hundred eight thousand, five hundred sixty-one".