861534819721 has 27 divisors (see below), whose sum is σ = 893036147367. Its totient is φ = 831137558160.

The previous prime is 861534819671. The next prime is 861534819731. The reversal of 861534819721 is 127918435168.

The square root of 861534819721 is 928189.

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

It can be written as a sum of positive squares in only one way, i.e., 621077967225 + 240456852496 = 788085^2 + 490364^2 .

It is not a de Polignac number, because 861534819721 - 2³⁵ = 827175081353 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (861534819731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 4083103306 + ... + 4083103516.

Almost surely, 2^861534819721 is an apocalyptic number.

861534819721 is the 928189-th square number.

861534819721 is the 464095-th centered octagonal number.

It is an amenable number.

861534819721 is a deficient number, since it is larger than the sum of its proper divisors (31501327646).

861534819721 is an frugal number, since it uses more digits than its factorization.

861534819721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 694 (or 347 counting only the distinct ones).

The product of its digits is 2903040, while the sum is 55.

The spelling of 861534819721 in words is "eight hundred sixty-one billion, five hundred thirty-four million, eight hundred nineteen thousand, seven hundred twenty-one".