81737991 has 20 divisors (see below), whose sum is σ = 122576872. Its totient is φ = 54280368.

The previous prime is 81737963. The next prime is 81738001. The reversal of 81737991 is 19973718.

It is not a de Polignac number, because 81737991 - 2⁵ = 81737959 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81737911) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 20616 + ... + 24258.

Almost surely, 2^81737991 is an apocalyptic number.

81737991 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

81737991 is a deficient number, since it is larger than the sum of its proper divisors (40838881).

81737991 is a wasteful number, since it uses less digits than its factorization.

81737991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3932 (or 3923 counting only the distinct ones).

The product of its digits is 95256, while the sum is 45.

The square root of 81737991 is about 9040.9065364044. The cubic root of 81737991 is about 433.9849340336.

It can be divided in two parts, 81737 and 991, that added together give a palindrome (82728).

The spelling of 81737991 in words is "eighty-one million, seven hundred thirty-seven thousand, nine hundred ninety-one".