81565646409 has 45 divisors (see below), whose sum is σ = 131992717989. Its totient is φ = 50173680960.

The previous prime is 81565646399. The next prime is 81565646411. The reversal of 81565646409 is 90464656518.

The square root of 81565646409 is 285597.

It is a perfect power (a square), and thus also a powerful number.

81565646409 is a `hidden beast` number, since 8 + 15 + 6 + 564 + 64 + 0 + 9 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 46831124025 + 34734522384 = 216405^2 + 186372^2 .

It is not a de Polignac number, because 81565646409 - 2⁵ = 81565646377 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81565646909) by changing a digit.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 33413629 + ... + 33416069.

Almost surely, 2^81565646409 is an apocalyptic number.

81565646409 is the 285597-th square number.

81565646409 is the 142799-th centered octagonal number.

It is an amenable number.

81565646409 is a deficient number, since it is larger than the sum of its proper divisors (50427071580).

81565646409 is an frugal number, since it uses more digits than its factorization.

81565646409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4920 (or 2457 counting only the distinct ones).

The product of its (nonzero) digits is 6220800, while the sum is 54.

It can be divided in two parts, 8156 and 5646409, that added together give a palindrome (5654565).

The spelling of 81565646409 in words is "eighty-one billion, five hundred sixty-five million, six hundred forty-six thousand, four hundred nine".