81645215 has 4 divisors (see below), whose sum is σ = 97974264. Its totient is φ = 65316168.

The previous prime is 81645211. The next prime is 81645229. The reversal of 81645215 is 51254618.

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 81645215 - 2² = 81645211 is a prime.

It is a super-2 number, since 2×81645215² = 13331882264792450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81645211) 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, 8164517 + ... + 8164526.

It is an arithmetic number, because the mean of its divisors is an integer number (24493566).

Almost surely, 2^81645215 is an apocalyptic number.

81645215 is a deficient number, since it is larger than the sum of its proper divisors (16329049).

81645215 is a wasteful number, since it uses less digits than its factorization.

81645215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16329048.

The product of its digits is 9600, while the sum is 32.

The square root of 81645215 is about 9035.7741782318. The cubic root of 81645215 is about 433.8206749218.

The spelling of 81645215 in words is "eighty-one million, six hundred forty-five thousand, two hundred fifteen".