81164591237 has 4 divisors (see below), whose sum is σ = 83358228876. Its totient is φ = 78970953600.

The previous prime is 81164591171. The next prime is 81164591239. The reversal of 81164591237 is 73219546118.

It is a Cunningham number, because it is equal to 284894²+1.

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 72627016036 + 8537575201 = 269494^2 + 92399^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81164591237 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81164591191 and 81164591200.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81164591239) 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, 1096818764 + ... + 1096818837.

It is an arithmetic number, because the mean of its divisors is an integer number (20839557219).

Almost surely, 2^81164591237 is an apocalyptic number.

It is an amenable number.

81164591237 is a deficient number, since it is larger than the sum of its proper divisors (2193637639).

81164591237 is a wasteful number, since it uses less digits than its factorization.

81164591237 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2193637638.

The product of its digits is 362880, while the sum is 47.

The spelling of 81164591237 in words is "eighty-one billion, one hundred sixty-four million, five hundred ninety-one thousand, two hundred thirty-seven".