81505213 has 4 divisors (see below), whose sum is σ = 81554940. Its totient is φ = 81455488.

The previous prime is 81505201. The next prime is 81505219. The reversal of 81505213 is 31250518.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 63075364 + 18429849 = 7942^2 + 4293^2 .

It is a cyclic number.

It is not a de Polignac number, because 81505213 - 2⁵ = 81505181 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81505219) 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, 22318 + ... + 25711.

It is an arithmetic number, because the mean of its divisors is an integer number (20388735).

Almost surely, 2^81505213 is an apocalyptic number.

It is an amenable number.

81505213 is a deficient number, since it is larger than the sum of its proper divisors (49727).

81505213 is a wasteful number, since it uses less digits than its factorization.

81505213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49726.

The product of its (nonzero) digits is 1200, while the sum is 25.

The square root of 81505213 is about 9028.0237593839. The cubic root of 81505213 is about 433.5725668484.

It can be divided in two parts, 81505 and 213, that added together give a palindrome (81718).

The spelling of 81505213 in words is "eighty-one million, five hundred five thousand, two hundred thirteen".