81649665 has 24 divisors (see below), whose sum is σ = 142084800. Its totient is φ = 43374624.

The previous prime is 81649663. The next prime is 81649679. The reversal of 81649665 is 56694618.

It is not a de Polignac number, because 81649665 - 2¹ = 81649663 is a prime.

It is a super-2 number, since 2×81649665² = 13333335589224450, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 81649665.

It is not an unprimeable number, because it can be changed into a prime (81649661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8386 + ... + 15284.

It is an arithmetic number, because the mean of its divisors is an integer number (5920200).

Almost surely, 2^81649665 is an apocalyptic number.

It is an amenable number.

81649665 is a deficient number, since it is larger than the sum of its proper divisors (60435135).

81649665 is a wasteful number, since it uses less digits than its factorization.

81649665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7173 (or 7170 counting only the distinct ones).

The product of its digits is 311040, while the sum is 45.

The square root of 81649665 is about 9036.0204183036. The cubic root of 81649665 is about 433.8285564489.

The spelling of 81649665 in words is "eighty-one million, six hundred forty-nine thousand, six hundred sixty-five".