821228647681 has 8 divisors (see below), whose sum is σ = 886673609640. Its totient is φ = 756108475392.

The previous prime is 821228647651. The next prime is 821228647711. The reversal of 821228647681 is 186746822128.

It is an interprime number because it is at equal distance from previous prime (821228647651) and next prime (821228647711).

It can be written as a sum of positive squares in 4 ways, for example, as 35124757056 + 786103890625 = 187416^2 + 886625^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 821228647681 - 2³⁷ = 683789694209 is a prime.

It is a super-2 number, since 2×821228647681² (a number of 25 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (821228647651) 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 7 ways as a sum of consecutive naturals, for example, 81192160 + ... + 81202273.

It is an arithmetic number, because the mean of its divisors is an integer number (110834201205).

Almost surely, 2^821228647681 is an apocalyptic number.

It is an amenable number.

821228647681 is a deficient number, since it is larger than the sum of its proper divisors (65444961959).

821228647681 is a wasteful number, since it uses less digits than its factorization.

821228647681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 162394835.

The product of its digits is 4128768, while the sum is 55.

The spelling of 821228647681 in words is "eight hundred twenty-one billion, two hundred twenty-eight million, six hundred forty-seven thousand, six hundred eighty-one".