81531997 has 4 divisors (see below), whose sum is σ = 82072096. Its totient is φ = 80991900.

The previous prime is 81531943. The next prime is 81532001. The reversal of 81531997 is 79913518.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81531997 - 2¹¹ = 81529949 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 (81531917) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 269823 + ... + 270124.

It is an arithmetic number, because the mean of its divisors is an integer number (20518024).

Almost surely, 2^81531997 is an apocalyptic number.

It is an amenable number.

81531997 is a deficient number, since it is larger than the sum of its proper divisors (540099).

81531997 is a wasteful number, since it uses less digits than its factorization.

81531997 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 540098.

The product of its digits is 68040, while the sum is 43.

The square root of 81531997 is about 9029.5070186583. The cubic root of 81531997 is about 433.6200547549.

It can be divided in two parts, 81531 and 997, that added together give a palindrome (82528).

The spelling of 81531997 in words is "eighty-one million, five hundred thirty-one thousand, nine hundred ninety-seven".