81640643 has 8 divisors (see below), whose sum is σ = 93361920. Its totient is φ = 69933960.

The previous prime is 81640627. The next prime is 81640649. The reversal of 81640643 is 34604618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81640643 - 2⁴ = 81640627 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81640649) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 14138 + ... + 19056.

It is an arithmetic number, because the mean of its divisors is an integer number (11670240).

Almost surely, 2^81640643 is an apocalyptic number.

81640643 is a deficient number, since it is larger than the sum of its proper divisors (11721277).

81640643 is a wasteful number, since it uses less digits than its factorization.

81640643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7297.

The product of its (nonzero) digits is 13824, while the sum is 32.

The square root of 81640643 is about 9035.5211803194. The cubic root of 81640643 is about 433.8125770186.

The spelling of 81640643 in words is "eighty-one million, six hundred forty thousand, six hundred forty-three".