81217915 has 4 divisors (see below), whose sum is σ = 97461504. Its totient is φ = 64974328.

The previous prime is 81217879. The next prime is 81217919. The reversal of 81217915 is 51971218.

It is a happy number.

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 81217915 - 2⁹ = 81217403 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81217919) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8121787 + ... + 8121796.

It is an arithmetic number, because the mean of its divisors is an integer number (24365376).

Almost surely, 2^81217915 is an apocalyptic number.

81217915 is a deficient number, since it is larger than the sum of its proper divisors (16243589).

81217915 is a wasteful number, since it uses less digits than its factorization.

81217915 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16243588.

The product of its digits is 5040, while the sum is 34.

The square root of 81217915 is about 9012.0982573427. The cubic root of 81217915 is about 433.0625333044.

The spelling of 81217915 in words is "eighty-one million, two hundred seventeen thousand, nine hundred fifteen".