81205251 has 4 divisors (see below), whose sum is σ = 108273672. Its totient is φ = 54136832.

The previous prime is 81205247. The next prime is 81205261. The reversal of 81205251 is 15250218.

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

It is a cyclic number.

It is not a de Polignac number, because 81205251 - 2² = 81205247 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81205211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13534206 + ... + 13534211.

It is an arithmetic number, because the mean of its divisors is an integer number (27068418).

Almost surely, 2^81205251 is an apocalyptic number.

81205251 is a deficient number, since it is larger than the sum of its proper divisors (27068421).

81205251 is a wasteful number, since it uses less digits than its factorization.

81205251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27068420.

The product of its (nonzero) digits is 800, while the sum is 24.

The square root of 81205251 is about 9011.3956188817. The cubic root of 81205251 is about 433.0400235375.

Adding to 81205251 its reverse (15250218), we get a palindrome (96455469).

The spelling of 81205251 in words is "eighty-one million, two hundred five thousand, two hundred fifty-one".