81565261 has 4 divisors (see below), whose sum is σ = 81600352. Its totient is φ = 81530172.

The previous prime is 81565259. The next prime is 81565273. The reversal of 81565261 is 16256518.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 16256518 = 2 ⋅8128259.

It is a cyclic number.

It is not a de Polignac number, because 81565261 - 2¹ = 81565259 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 (81565361) 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, 13791 + ... + 18796.

It is an arithmetic number, because the mean of its divisors is an integer number (20400088).

Almost surely, 2^81565261 is an apocalyptic number.

It is an amenable number.

81565261 is a deficient number, since it is larger than the sum of its proper divisors (35091).

81565261 is a wasteful number, since it uses less digits than its factorization.

81565261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35090.

The product of its digits is 14400, while the sum is 34.

The square root of 81565261 is about 9031.3487918472. The cubic root of 81565261 is about 433.6790171945.

The spelling of 81565261 in words is "eighty-one million, five hundred sixty-five thousand, two hundred sixty-one".