81664069 has 8 divisors (see below), whose sum is σ = 84439800. Its totient is φ = 78918336.

The previous prime is 81664067. The next prime is 81664111. The reversal of 81664069 is 96046618.

It can be written as a sum of positive squares in 4 ways, for example, as 7049025 + 74615044 = 2655^2 + 8638^2 .

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

It is not a de Polignac number, because 81664069 - 2¹ = 81664067 is a prime.

It is a super-2 number, since 2×81664069² = 13338040331273522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81664061) 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, 1894 + ... + 12919.

It is an arithmetic number, because the mean of its divisors is an integer number (10554975).

Almost surely, 2^81664069 is an apocalyptic number.

It is an amenable number.

81664069 is a deficient number, since it is larger than the sum of its proper divisors (2775731).

81664069 is a wasteful number, since it uses less digits than its factorization.

81664069 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14999.

The product of its (nonzero) digits is 62208, while the sum is 40.

The square root of 81664069 is about 9036.8174154400. The cubic root of 81664069 is about 433.8540658376.

The spelling of 81664069 in words is "eighty-one million, six hundred sixty-four thousand, sixty-nine".