81821386 has 4 divisors (see below), whose sum is σ = 122732082. Its totient is φ = 40910692.

The previous prime is 81821371. The next prime is 81821387. The reversal of 81821386 is 68312818.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 63920025 + 17901361 = 7995^2 + 4231^2 .

It is not an unprimeable number, because it can be changed into a prime (81821387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20455345 + ... + 20455348.

Almost surely, 2^81821386 is an apocalyptic number.

81821386 is a deficient number, since it is larger than the sum of its proper divisors (40910696).

81821386 is a wasteful number, since it uses less digits than its factorization.

81821386 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40910695.

The product of its digits is 18432, while the sum is 37.

The square root of 81821386 is about 9045.5174534130. The cubic root of 81821386 is about 434.1324781212.

The spelling of 81821386 in words is "eighty-one million, eight hundred twenty-one thousand, three hundred eighty-six".