81671729 has 2 divisors, whose sum is σ = 81671730. Its totient is φ = 81671728.

The previous prime is 81671683. The next prime is 81671771. The reversal of 81671729 is 92717618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 73960000 + 7711729 = 8600^2 + 2777^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81671729 is a prime.

It is not a weakly prime, because it can be changed into another prime (81671129) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40835864 + 40835865.

It is an arithmetic number, because the mean of its divisors is an integer number (40835865).

Almost surely, 2^81671729 is an apocalyptic number.

It is an amenable number.

81671729 is a deficient number, since it is larger than the sum of its proper divisors (1).

81671729 is an equidigital number, since it uses as much as digits as its factorization.

81671729 is an evil number, because the sum of its binary digits is even.

The product of its digits is 42336, while the sum is 41.

The square root of 81671729 is about 9037.2412272773. The cubic root of 81671729 is about 433.8676304251.

The spelling of 81671729 in words is "eighty-one million, six hundred seventy-one thousand, seven hundred twenty-nine".