81911515 has 16 divisors (see below), whose sum is σ = 116210880. Its totient is φ = 54230400.

The previous prime is 81911513. The next prime is 81911537. The reversal of 81911515 is 51511918.

It is not a de Polignac number, because 81911515 - 2¹ = 81911513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81911513) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 39336 + ... + 41365.

It is an arithmetic number, because the mean of its divisors is an integer number (7263180).

Almost surely, 2^81911515 is an apocalyptic number.

81911515 is a deficient number, since it is larger than the sum of its proper divisors (34299365).

81911515 is a wasteful number, since it uses less digits than its factorization.

81911515 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80742.

The product of its digits is 1800, while the sum is 31.

The square root of 81911515 is about 9050.4980525936. The cubic root of 81911515 is about 434.2918234542.

The spelling of 81911515 in words is "eighty-one million, nine hundred eleven thousand, five hundred fifteen".