81684121 has 4 divisors (see below), whose sum is σ = 82447632. Its totient is φ = 80920612.

The previous prime is 81684107. The next prime is 81684131. The reversal of 81684121 is 12148618.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81684121 - 2⁷ = 81683993 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81684131) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 381595 + ... + 381808.

It is an arithmetic number, because the mean of its divisors is an integer number (20611908).

Almost surely, 2^81684121 is an apocalyptic number.

It is an amenable number.

81684121 is a deficient number, since it is larger than the sum of its proper divisors (763511).

81684121 is a wasteful number, since it uses less digits than its factorization.

81684121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 763510.

The product of its digits is 3072, while the sum is 31.

The square root of 81684121 is about 9037.9268087322. The cubic root of 81684121 is about 433.8895728028.

The spelling of 81684121 in words is "eighty-one million, six hundred eighty-four thousand, one hundred twenty-one".