813121220 has 24 divisors (see below), whose sum is σ = 1807999704. Its totient is φ = 306116096.

The previous prime is 813121201. The next prime is 813121223. The reversal of 813121220 is 22121318.

It can be written as a sum of positive squares in 4 ways, for example, as 26543104 + 786578116 = 5152^2 + 28046^2 .

It is a super-2 number, since 2×813121220² = 1322332236828576800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 813121192 and 813121201.

It is not an unprimeable number, because it can be changed into a prime (813121223) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1195427 + ... + 1196106.

It is an arithmetic number, because the mean of its divisors is an integer number (75333321).

Almost surely, 2^813121220 is an apocalyptic number.

It is an amenable number.

813121220 is an abundant number, since it is smaller than the sum of its proper divisors (994878484).

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

813121220 is a wasteful number, since it uses less digits than its factorization.

813121220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2391559 (or 2391557 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 20.

The square root of 813121220 is about 28515.2804650419. The cubic root of 813121220 is about 933.3655450901.

Adding to 813121220 its reverse (22121318), we get a palindrome (835242538).

The spelling of 813121220 in words is "eight hundred thirteen million, one hundred twenty-one thousand, two hundred twenty".