821142256561 has 15 divisors (see below), whose sum is σ = 903371500155. Its totient is φ = 746393281920.

The previous prime is 821142256553. The next prime is 821142256591. The reversal of 821142256561 is 165652241128.

The square root of 821142256561 is 906169.

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., 412974602161 + 408167654400 = 642631^2 + 638880^2 .

It is not a de Polignac number, because 821142256561 - 2³ = 821142256553 is a prime.

It is a super-3 number, since 3×821142256561³ (a number of 37 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (821142256531) by changing a digit.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 109642705 + ... + 109650193.

It is an arithmetic number, because the mean of its divisors is an integer number (60224766677).

Almost surely, 2^821142256561 is an apocalyptic number.

821142256561 is the 906169-th square number.

821142256561 is the 453085-th centered octagonal number.

It is an amenable number.

821142256561 is a deficient number, since it is larger than the sum of its proper divisors (82229243594).

821142256561 is an frugal number, since it uses more digits than its factorization.

821142256561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15022 (or 7500 counting only the distinct ones).

The product of its digits is 230400, while the sum is 43.

Adding to 821142256561 its reverse (165652241128), we get a palindrome (986794497689).

The spelling of 821142256561 in words is "eight hundred twenty-one billion, one hundred forty-two million, two hundred fifty-six thousand, five hundred sixty-one".