819647561 has 4 divisors (see below), whose sum is σ = 847911300. Its totient is φ = 791383824.

The previous prime is 819647557. The next prime is 819647567. The reversal of 819647561 is 165746918.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 551310400 + 268337161 = 23480^2 + 16381^2 .

It is a cyclic number.

It is not a de Polignac number, because 819647561 - 2² = 819647557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (819647567) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14131826 + ... + 14131883.

It is an arithmetic number, because the mean of its divisors is an integer number (211977825).

Almost surely, 2^819647561 is an apocalyptic number.

It is an amenable number.

819647561 is a deficient number, since it is larger than the sum of its proper divisors (28263739).

819647561 is a wasteful number, since it uses less digits than its factorization.

819647561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28263738.

The product of its digits is 362880, while the sum is 47.

The square root of 819647561 is about 28629.4876132983. The cubic root of 819647561 is about 935.8560457656.

The spelling of 819647561 in words is "eight hundred nineteen million, six hundred forty-seven thousand, five hundred sixty-one".