81312509 has 4 divisors (see below), whose sum is σ = 81330816. Its totient is φ = 81294204.

The previous prime is 81312503. The next prime is 81312551. The reversal of 81312509 is 90521318.

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.

It is a cyclic number.

It is not a de Polignac number, because 81312509 - 2⁴ = 81312493 is a prime.

It is a super-2 number, since 2×81312509² = 13223448239750162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81312503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2222 + ... + 12944.

It is an arithmetic number, because the mean of its divisors is an integer number (20332704).

Almost surely, 2^81312509 is an apocalyptic number.

It is an amenable number.

81312509 is a deficient number, since it is larger than the sum of its proper divisors (18307).

81312509 is a wasteful number, since it uses less digits than its factorization.

81312509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18306.

The product of its (nonzero) digits is 2160, while the sum is 29.

The square root of 81312509 is about 9017.3448974740. The cubic root of 81312509 is about 433.2305964861.

The spelling of 81312509 in words is "eighty-one million, three hundred twelve thousand, five hundred nine".