81631218 has 16 divisors (see below), whose sum is σ = 163429056. Its totient is φ = 27182640.

The previous prime is 81631217. The next prime is 81631219. The reversal of 81631218 is 81213618.

It is an interprime number because it is at equal distance from previous prime (81631217) and next prime (81631219).

It is not an unprimeable number, because it can be changed into a prime (81631211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 46 + ... + 12777.

It is an arithmetic number, because the mean of its divisors is an integer number (10214316).

Almost surely, 2^81631218 is an apocalyptic number.

81631218 is an abundant number, since it is smaller than the sum of its proper divisors (81797838).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81631218 is a wasteful number, since it uses less digits than its factorization.

81631218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13889.

The product of its digits is 2304, while the sum is 30.

The square root of 81631218 is about 9034.9996126176. Note that the first 3 decimals coincide. The cubic root of 81631218 is about 433.7958825523.

The spelling of 81631218 in words is "eighty-one million, six hundred thirty-one thousand, two hundred eighteen".