81644003581 has 12 divisors (see below), whose sum is σ = 93474492832. Its totient is φ = 69855334344.

The previous prime is 81644003569. The next prime is 81644003593. The reversal of 81644003581 is 18530044618.

It is an interprime number because it is at equal distance from previous prime (81644003569) and next prime (81644003593).

It is not a de Polignac number, because 81644003581 - 2⁵ = 81644003549 is a prime.

It is a super-2 number, since 2×81644003581² (a number of 23 digits) contains 22 as substring.

It is a hoax number, since the sum of its digits (40) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81644003081) 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 11 ways as a sum of consecutive naturals, for example, 19167630 + ... + 19171888.

Almost surely, 2^81644003581 is an apocalyptic number.

It is an amenable number.

81644003581 is a deficient number, since it is larger than the sum of its proper divisors (11830489251).

81644003581 is an frugal number, since it uses more digits than its factorization.

81644003581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9168 (or 4909 counting only the distinct ones).

The product of its (nonzero) digits is 92160, while the sum is 40.

The spelling of 81644003581 in words is "eighty-one billion, six hundred forty-four million, three thousand, five hundred eighty-one".