821217809957 has 4 divisors (see below), whose sum is σ = 821220759756. Its totient is φ = 821214860160.

The previous prime is 821217809903. The next prime is 821217809959. The reversal of 821217809957 is 759908712128.

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 550483866916 + 270733943041 = 741946^2 + 520321^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-821217809957 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 821217809896 and 821217809905.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821217809959) 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, 1008044 + ... + 1630517.

It is an arithmetic number, because the mean of its divisors is an integer number (205305189939).

Almost surely, 2^821217809957 is an apocalyptic number.

It is an amenable number.

821217809957 is a deficient number, since it is larger than the sum of its proper divisors (2949799).

821217809957 is a wasteful number, since it uses less digits than its factorization.

821217809957 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2949798.

The product of its (nonzero) digits is 5080320, while the sum is 59.

The spelling of 821217809957 in words is "eight hundred twenty-one billion, two hundred seventeen million, eight hundred nine thousand, nine hundred fifty-seven".