81521515 has 4 divisors (see below), whose sum is σ = 97825824. Its totient is φ = 65217208.

The previous prime is 81521501. The next prime is 81521527. The reversal of 81521515 is 51512518.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 51512518 = 2 ⋅25756259.

It is a cyclic number.

It is not a de Polignac number, because 81521515 - 2⁵ = 81521483 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8152147 + ... + 8152156.

It is an arithmetic number, because the mean of its divisors is an integer number (24456456).

Almost surely, 2^81521515 is an apocalyptic number.

81521515 is a deficient number, since it is larger than the sum of its proper divisors (16304309).

81521515 is a wasteful number, since it uses less digits than its factorization.

81521515 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16304308.

The product of its digits is 2000, while the sum is 28.

The square root of 81521515 is about 9028.9265696427. The cubic root of 81521515 is about 433.6014714568.

The spelling of 81521515 in words is "eighty-one million, five hundred twenty-one thousand, five hundred fifteen".