81221515 has 8 divisors (see below), whose sum is σ = 98839008. Its totient is φ = 64061760.

The previous prime is 81221507. The next prime is 81221527. The reversal of 81221515 is 51512218.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81221515 - 2³ = 81221507 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81221515.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 114042 + ... + 114751.

It is an arithmetic number, because the mean of its divisors is an integer number (12354876).

Almost surely, 2^81221515 is an apocalyptic number.

81221515 is a deficient number, since it is larger than the sum of its proper divisors (17617493).

81221515 is a wasteful number, since it uses less digits than its factorization.

81221515 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 228869.

The product of its digits is 800, while the sum is 25.

The square root of 81221515 is about 9012.2979866403. The cubic root of 81221515 is about 433.0689317371.

The spelling of 81221515 in words is "eighty-one million, two hundred twenty-one thousand, five hundred fifteen".