820011723561 has 6 divisors (see below), whose sum is σ = 1184461378490. Its totient is φ = 546674482368.

The previous prime is 820011723533. The next prime is 820011723571. The reversal of 820011723561 is 165327110028.

820011723561 is a `hidden beast` number, since 8 + 20 + 0 + 1 + 1 + 72 + 3 + 561 = 666.

It can be written as a sum of positive squares in only one way, i.e., 649241120025 + 170770603536 = 805755^2 + 413244^2 .

It is not a de Polignac number, because 820011723561 - 2⁹ = 820011723049 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (820011723571) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 45556206856 + ... + 45556206873.

Almost surely, 2^820011723561 is an apocalyptic number.

It is an amenable number.

820011723561 is a deficient number, since it is larger than the sum of its proper divisors (364449654929).

820011723561 is a wasteful number, since it uses less digits than its factorization.

820011723561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91112413735 (or 91112413732 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

Adding to 820011723561 its reverse (165327110028), we get a palindrome (985338833589).

The spelling of 820011723561 in words is "eight hundred twenty billion, eleven million, seven hundred twenty-three thousand, five hundred sixty-one".