81520171 has 2 divisors, whose sum is σ = 81520172. Its totient is φ = 81520170.

The previous prime is 81520169. The next prime is 81520199. The reversal of 81520171 is 17102518.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81520171 - 2¹ = 81520169 is a prime.

Together with 81520169, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81524171) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40760085 + 40760086.

It is an arithmetic number, because the mean of its divisors is an integer number (40760086).

Almost surely, 2^81520171 is an apocalyptic number.

81520171 is a deficient number, since it is larger than the sum of its proper divisors (1).

81520171 is an equidigital number, since it uses as much as digits as its factorization.

81520171 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 560, while the sum is 25.

The square root of 81520171 is about 9028.8521418838. The cubic root of 81520171 is about 433.5990885947.

Adding to 81520171 its reverse (17102518), we get a palindrome (98622689).

The spelling of 81520171 in words is "eighty-one million, five hundred twenty thousand, one hundred seventy-one".