81215805 has 48 divisors (see below), whose sum is σ = 147853440. Its totient is φ = 37994880.

The previous prime is 81215789. The next prime is 81215807. The reversal of 81215805 is 50851218.

It is not a de Polignac number, because 81215805 - 2⁴ = 81215789 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81215807) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 51864 + ... + 53406.

It is an arithmetic number, because the mean of its divisors is an integer number (3080280).

Almost surely, 2^81215805 is an apocalyptic number.

It is an amenable number.

81215805 is a deficient number, since it is larger than the sum of its proper divisors (66637635).

81215805 is a wasteful number, since it uses less digits than its factorization.

81215805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1602 (or 1591 counting only the distinct ones).

The product of its (nonzero) digits is 3200, while the sum is 30.

The square root of 81215805 is about 9011.9811917247. The cubic root of 81215805 is about 433.0587830240.

The spelling of 81215805 in words is "eighty-one million, two hundred fifteen thousand, eight hundred five".