821911561 has 3 divisors (see below), whose sum is σ = 821940231. Its totient is φ = 821882892.

The previous prime is 821911553. The next prime is 821911603. The reversal of 821911561 is 165119128.

The square root of 821911561 is 28669.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 664659961 + 157251600 = 25781^2 + 12540^2 .

It is not a de Polignac number, because 821911561 - 2³ = 821911553 is a prime.

It is a super-2 number, since 2×821911561² = 1351077228210913442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (821911501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 14335 + ... + 43003.

It is an arithmetic number, because the mean of its divisors is an integer number (273980077).

Almost surely, 2^821911561 is an apocalyptic number.

821911561 is the 28669-th square number.

821911561 is the 14335-th centered octagonal number.

It is an amenable number.

821911561 is a deficient number, since it is larger than the sum of its proper divisors (28670).

821911561 is an frugal number, since it uses more digits than its factorization.

821911561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57338 (or 28669 counting only the distinct ones).

The product of its digits is 4320, while the sum is 34.

The cubic root of 821911561 is about 936.7169158815.

The spelling of 821911561 in words is "eight hundred twenty-one million, nine hundred eleven thousand, five hundred sixty-one".