81991994 has 36 divisors (see below), whose sum is σ = 145978254. Its totient is φ = 34437312.

The previous prime is 81991981. The next prime is 81991999. The reversal of 81991994 is 49919918.

It can be written as a sum of positive squares in 3 ways, for example, as 67650625 + 14341369 = 8225^2 + 3787^2 .

It is not an unprimeable number, because it can be changed into a prime (81991999) 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 17 ways as a sum of consecutive naturals, for example, 522164 + ... + 522320.

Almost surely, 2^81991994 is an apocalyptic number.

81991994 is a deficient number, since it is larger than the sum of its proper divisors (63986260).

81991994 is a wasteful number, since it uses less digits than its factorization.

81991994 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 319 (or 239 counting only the distinct ones).

The product of its digits is 209952, while the sum is 50.

The square root of 81991994 is about 9054.9430699480. The cubic root of 81991994 is about 434.4340091253.

The spelling of 81991994 in words is "eighty-one million, nine hundred ninety-one thousand, nine hundred ninety-four".