81661071 has 16 divisors (see below), whose sum is σ = 112896000. Its totient is φ = 52442208.

The previous prime is 81661067. The next prime is 81661087. The reversal of 81661071 is 17016618.

It is a happy number.

It is not a de Polignac number, because 81661071 - 2² = 81661067 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81661001) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 51330 + ... + 52896.

It is an arithmetic number, because the mean of its divisors is an integer number (7056000).

Almost surely, 2^81661071 is an apocalyptic number.

81661071 is a deficient number, since it is larger than the sum of its proper divisors (31234929).

81661071 is a wasteful number, since it uses less digits than its factorization.

81661071 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2198.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 81661071 is about 9036.6515369356. The cubic root of 81661071 is about 433.8487566466.

Adding to 81661071 its reverse (17016618), we get a palindrome (98677689).

The spelling of 81661071 in words is "eighty-one million, six hundred sixty-one thousand, seventy-one".