81641609 has 4 divisors (see below), whose sum is σ = 93304704. Its totient is φ = 69978516.

The previous prime is 81641603. The next prime is 81641617. The reversal of 81641609 is 90614618.

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 a de Polignac number, because none of the positive numbers 2^k-81641609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81641603) 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, 5831537 + ... + 5831550.

It is an arithmetic number, because the mean of its divisors is an integer number (23326176).

Almost surely, 2^81641609 is an apocalyptic number.

It is an amenable number.

81641609 is a deficient number, since it is larger than the sum of its proper divisors (11663095).

81641609 is a wasteful number, since it uses less digits than its factorization.

81641609 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11663094.

The product of its (nonzero) digits is 10368, while the sum is 35.

The square root of 81641609 is about 9035.5746358491. The cubic root of 81641609 is about 433.8142880181.

The spelling of 81641609 in words is "eighty-one million, six hundred forty-one thousand, six hundred nine".