81211565 has 4 divisors (see below), whose sum is σ = 97453884. Its totient is φ = 64969248.

The previous prime is 81211523. The next prime is 81211573. The reversal of 81211565 is 56511218.

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 25664356 + 55547209 = 5066^2 + 7453^2 .

It is a cyclic number.

It is not a de Polignac number, because 81211565 - 2⁸ = 81211309 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8121152 + ... + 8121161.

It is an arithmetic number, because the mean of its divisors is an integer number (24363471).

Almost surely, 2^81211565 is an apocalyptic number.

It is an amenable number.

81211565 is a deficient number, since it is larger than the sum of its proper divisors (16242319).

81211565 is a wasteful number, since it uses less digits than its factorization.

81211565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16242318.

The product of its digits is 2400, while the sum is 29.

The square root of 81211565 is about 9011.7459462637. The cubic root of 81211565 is about 433.0512467192.

The spelling of 81211565 in words is "eighty-one million, two hundred eleven thousand, five hundred sixty-five".