81991562 has 4 divisors (see below), whose sum is σ = 122987346. Its totient is φ = 40995780.

The previous prime is 81991543. The next prime is 81991601. The reversal of 81991562 is 26519918.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 62552281 + 19439281 = 7909^2 + 4409^2 .

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 20497889 + ... + 20497892.

Almost surely, 2^81991562 is an apocalyptic number.

81991562 is a deficient number, since it is larger than the sum of its proper divisors (40995784).

81991562 is a wasteful number, since it uses less digits than its factorization.

81991562 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40995783.

The product of its digits is 38880, while the sum is 41.

The square root of 81991562 is about 9054.9192155425. The cubic root of 81991562 is about 434.4332461410.

The spelling of 81991562 in words is "eighty-one million, nine hundred ninety-one thousand, five hundred sixty-two".