81564397 has 4 divisors (see below), whose sum is σ = 85857280. Its totient is φ = 77271516.

The previous prime is 81564389. The next prime is 81564401. The reversal of 81564397 is 79346518.

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 81564397 - 2³ = 81564389 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 (81564337) 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, 2146413 + ... + 2146450.

It is an arithmetic number, because the mean of its divisors is an integer number (21464320).

Almost surely, 2^81564397 is an apocalyptic number.

It is an amenable number.

81564397 is a deficient number, since it is larger than the sum of its proper divisors (4292883).

81564397 is a wasteful number, since it uses less digits than its factorization.

81564397 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4292882.

The product of its digits is 181440, while the sum is 43.

The square root of 81564397 is about 9031.3009583337. The cubic root of 81564397 is about 433.6774859054.

The spelling of 81564397 in words is "eighty-one million, five hundred sixty-four thousand, three hundred ninety-seven".