81191720 has 16 divisors (see below), whose sum is σ = 182681460. Its totient is φ = 32476672.

The previous prime is 81191717. The next prime is 81191741. The reversal of 81191720 is 2719118.

It can be written as a sum of positive squares in 2 ways, for example, as 77404804 + 3786916 = 8798^2 + 1946^2 .

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 in 3 ways as a sum of consecutive naturals, for example, 1014857 + ... + 1014936.

Almost surely, 2^81191720 is an apocalyptic number.

It is an amenable number.

81191720 is an abundant number, since it is smaller than the sum of its proper divisors (101489740).

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

81191720 is a wasteful number, since it uses less digits than its factorization.

81191720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2029804 (or 2029800 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 29.

The square root of 81191720 is about 9010.6448159940. The cubic root of 81191720 is about 433.0159701257.

The spelling of 81191720 in words is "eighty-one million, one hundred ninety-one thousand, seven hundred twenty".