81901665 has 64 divisors (see below), whose sum is σ = 155934720. Its totient is φ = 40642560.

The previous prime is 81901649. The next prime is 81901667. The reversal of 81901665 is 56610918.

It is not a de Polignac number, because 81901665 - 2⁴ = 81901649 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81901667) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 291325 + ... + 291605.

It is an arithmetic number, because the mean of its divisors is an integer number (2436480).

Almost surely, 2^81901665 is an apocalyptic number.

81901665 is a gapful number since it is divisible by the number (85) formed by its first and last digit.

It is an amenable number.

81901665 is a deficient number, since it is larger than the sum of its proper divisors (74033055).

81901665 is a wasteful number, since it uses less digits than its factorization.

81901665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439 (or 433 counting only the distinct ones).

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

The square root of 81901665 is about 9049.9538672857. The cubic root of 81901665 is about 434.2744146445.

The spelling of 81901665 in words is "eighty-one million, nine hundred one thousand, six hundred sixty-five".