81185261 has 4 divisors (see below), whose sum is σ = 81258300. Its totient is φ = 81112224.

The previous prime is 81185243. The next prime is 81185263. The reversal of 81185261 is 16258118.

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 23136100 + 58049161 = 4810^2 + 7619^2 .

It is a cyclic number.

It is not a de Polignac number, because 81185261 - 2²² = 76990957 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 (81185263) 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, 34826 + ... + 37083.

It is an arithmetic number, because the mean of its divisors is an integer number (20314575).

Almost surely, 2^81185261 is an apocalyptic number.

It is an amenable number.

81185261 is a deficient number, since it is larger than the sum of its proper divisors (73039).

81185261 is a wasteful number, since it uses less digits than its factorization.

81185261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 73038.

The product of its digits is 3840, while the sum is 32.

The square root of 81185261 is about 9010.2863994437. The cubic root of 81185261 is about 433.0044873279.

The spelling of 81185261 in words is "eighty-one million, one hundred eighty-five thousand, two hundred sixty-one".