811561820 has 24 divisors (see below), whose sum is σ = 1793979600. Its totient is φ = 307539072.

The previous prime is 811561787. The next prime is 811561847. The reversal of 811561820 is 28165118.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1067465 + ... + 1068224.

It is an arithmetic number, because the mean of its divisors is an integer number (74749150).

Almost surely, 2^811561820 is an apocalyptic number.

It is an amenable number.

811561820 is an abundant number, since it is smaller than the sum of its proper divisors (982417780).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

811561820 is a wasteful number, since it uses less digits than its factorization.

811561820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2135717 (or 2135715 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 32.

The square root of 811561820 is about 28487.9241082954. The cubic root of 811561820 is about 932.7684952563.

The spelling of 811561820 in words is "eight hundred eleven million, five hundred sixty-one thousand, eight hundred twenty".