81639161 has 4 divisors (see below), whose sum is σ = 81756324. Its totient is φ = 81522000.

The previous prime is 81639157. The next prime is 81639163. The reversal of 81639161 is 16193618.

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

It can be written as a sum of positive squares in 2 ways, for example, as 35331136 + 46308025 = 5944^2 + 6805^2 .

It is a cyclic number.

It is not a de Polignac number, because 81639161 - 2² = 81639157 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81639163) 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, 57530 + ... + 58931.

It is an arithmetic number, because the mean of its divisors is an integer number (20439081).

Almost surely, 2^81639161 is an apocalyptic number.

It is an amenable number.

81639161 is a deficient number, since it is larger than the sum of its proper divisors (117163).

81639161 is a wasteful number, since it uses less digits than its factorization.

81639161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117162.

The product of its digits is 7776, while the sum is 35.

The square root of 81639161 is about 9035.4391702894. The cubic root of 81639161 is about 433.8099520428.

The spelling of 81639161 in words is "eighty-one million, six hundred thirty-nine thousand, one hundred sixty-one".