81910665 has 12 divisors (see below), whose sum is σ = 141978564. Its totient is φ = 43685664.

The previous prime is 81910651. The next prime is 81910667. The reversal of 81910665 is 56601918.

It can be written as a sum of positive squares in 2 ways, for example, as 11148921 + 70761744 = 3339^2 + 8412^2 .

It is not a de Polignac number, because 81910665 - 2¹² = 81906569 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81910667) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 910074 + ... + 910163.

It is an arithmetic number, because the mean of its divisors is an integer number (11831547).

Almost surely, 2^81910665 is an apocalyptic number.

It is an amenable number.

81910665 is a deficient number, since it is larger than the sum of its proper divisors (60067899).

81910665 is a wasteful number, since it uses less digits than its factorization.

81910665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1820248 (or 1820245 counting only the distinct ones).

The product of its (nonzero) digits is 12960, while the sum is 36.

The square root of 81910665 is about 9050.4510937301. The cubic root of 81910665 is about 434.2903212262.

The spelling of 81910665 in words is "eighty-one million, nine hundred ten thousand, six hundred sixty-five".