81861515 has 4 divisors (see below), whose sum is σ = 98233824. Its totient is φ = 65489208.

The previous prime is 81861487. The next prime is 81861517. The reversal of 81861515 is 51516818.

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

It is a cyclic number.

It is not a de Polignac number, because 81861515 - 2¹⁴ = 81845131 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81861517) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8186147 + ... + 8186156.

It is an arithmetic number, because the mean of its divisors is an integer number (24558456).

Almost surely, 2^81861515 is an apocalyptic number.

81861515 is a deficient number, since it is larger than the sum of its proper divisors (16372309).

81861515 is a wasteful number, since it uses less digits than its factorization.

81861515 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16372308.

The product of its digits is 9600, while the sum is 35.

The square root of 81861515 is about 9047.7353520094. The cubic root of 81861515 is about 434.2034394178.

The spelling of 81861515 in words is "eighty-one million, eight hundred sixty-one thousand, five hundred fifteen".