81991637 has 8 divisors (see below), whose sum is σ = 100912896. Its totient is φ = 64872432.

The previous prime is 81991627. The next prime is 81991649. The reversal of 81991637 is 73619918.

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

It is a cyclic number.

It is not a de Polignac number, because 81991637 - 2¹⁰ = 81990613 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81991627) 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, 450413 + ... + 450594.

It is an arithmetic number, because the mean of its divisors is an integer number (12614112).

Almost surely, 2^81991637 is an apocalyptic number.

It is an amenable number.

81991637 is a deficient number, since it is larger than the sum of its proper divisors (18921259).

81991637 is a wasteful number, since it uses less digits than its factorization.

81991637 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 901027.

The product of its digits is 81648, while the sum is 44.

The square root of 81991637 is about 9054.9233569368. The cubic root of 81991637 is about 434.4333786037.

It can be divided in two parts, 81991 and 637, that added together give a palindrome (82628).

The spelling of 81991637 in words is "eighty-one million, nine hundred ninety-one thousand, six hundred thirty-seven".