81813971 has 4 divisors (see below), whose sum is σ = 82657512. Its totient is φ = 80970432.

The previous prime is 81813961. The next prime is 81813973. The reversal of 81813971 is 17931818.

81813971 = T₁₂₅₀ + T₁₂₅₁ + ... + T₁₃₄₆.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81813971 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81813973) 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, 421625 + ... + 421818.

It is an arithmetic number, because the mean of its divisors is an integer number (20664378).

Almost surely, 2^81813971 is an apocalyptic number.

81813971 is a deficient number, since it is larger than the sum of its proper divisors (843541).

81813971 is an equidigital number, since it uses as much as digits as its factorization.

81813971 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 843540.

The product of its digits is 12096, while the sum is 38.

The square root of 81813971 is about 9045.1075726052. The cubic root of 81813971 is about 434.1193634180.

The spelling of 81813971 in words is "eighty-one million, eight hundred thirteen thousand, nine hundred seventy-one".