816661118021 has 6 divisors (see below), whose sum is σ = 949993545510. Its totient is φ = 699995243976.

The previous prime is 816661118017. The next prime is 816661118027. The reversal of 816661118021 is 120811166618.

It can be written as a sum of positive squares in only one way, i.e., 443175129796 + 373485988225 = 665714^2 + 611135^2 .

It is not a de Polignac number, because 816661118021 - 2² = 816661118017 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 816661118021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (816661118027) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8333276666 + ... + 8333276763.

It is an arithmetic number, because the mean of its divisors is an integer number (158332257585).

Almost surely, 2^816661118021 is an apocalyptic number.

It is an amenable number.

816661118021 is a deficient number, since it is larger than the sum of its proper divisors (133332427489).

816661118021 is a wasteful number, since it uses less digits than its factorization.

816661118021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16666553443 (or 16666553436 counting only the distinct ones).

The product of its (nonzero) digits is 27648, while the sum is 41.

The spelling of 816661118021 in words is "eight hundred sixteen billion, six hundred sixty-one million, one hundred eighteen thousand, twenty-one".