81821138 has 8 divisors (see below), whose sum is σ = 140264832. Its totient is φ = 35066196.

The previous prime is 81821123. The next prime is 81821167. The reversal of 81821138 is 83112818.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2922170 + ... + 2922197.

It is an arithmetic number, because the mean of its divisors is an integer number (17533104).

Almost surely, 2^81821138 is an apocalyptic number.

81821138 is a deficient number, since it is larger than the sum of its proper divisors (58443694).

81821138 is a wasteful number, since it uses less digits than its factorization.

81821138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5844376.

The product of its digits is 3072, while the sum is 32.

The square root of 81821138 is about 9045.5037449553. The cubic root of 81821138 is about 434.1320395033.

The spelling of 81821138 in words is "eighty-one million, eight hundred twenty-one thousand, one hundred thirty-eight".