81213320 has 32 divisors (see below), whose sum is σ = 183026520. Its totient is φ = 32432640.

The previous prime is 81213317. The next prime is 81213367. The reversal of 81213320 is 2331218.

It can be written as a sum of positive squares in 4 ways, for example, as 65642404 + 15570916 = 8102^2 + 3946^2 .

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 = 81213292 and 81213301.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31604 + ... + 34076.

Almost surely, 2^81213320 is an apocalyptic number.

It is an amenable number.

81213320 is an abundant number, since it is smaller than the sum of its proper divisors (101813200).

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

81213320 is a wasteful number, since it uses less digits than its factorization.

81213320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3305 (or 3301 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 81213320 is about 9011.8433186557. The cubic root of 81213320 is about 433.0543661413.

Adding to 81213320 its reverse (2331218), we get a palindrome (83544538).

The spelling of 81213320 in words is "eighty-one million, two hundred thirteen thousand, three hundred twenty".