81640849 has 4 divisors (see below), whose sum is σ = 82068480. Its totient is φ = 81213220.

The previous prime is 81640847. The next prime is 81640859. The reversal of 81640849 is 94804618.

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 81640849 - 2¹ = 81640847 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81640843) 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, 213529 + ... + 213910.

It is an arithmetic number, because the mean of its divisors is an integer number (20517120).

Almost surely, 2^81640849 is an apocalyptic number.

It is an amenable number.

81640849 is a deficient number, since it is larger than the sum of its proper divisors (427631).

81640849 is a wasteful number, since it uses less digits than its factorization.

81640849 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 427630.

The product of its (nonzero) digits is 55296, while the sum is 40.

The square root of 81640849 is about 9035.5325797653. The cubic root of 81640849 is about 433.8129418913.

The spelling of 81640849 in words is "eighty-one million, six hundred forty thousand, eight hundred forty-nine".