81720418 has 16 divisors (see below), whose sum is σ = 132189120. Its totient is φ = 37665936.

The previous prime is 81720409. The next prime is 81720427. The reversal of 81720418 is 81402718.

It is an interprime number because it is at equal distance from previous prime (81720409) and next prime (81720427).

It is a self number, because there is not a number n which added to its sum of digits gives 81720418.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 22963 + ... + 26281.

It is an arithmetic number, because the mean of its divisors is an integer number (8261820).

Almost surely, 2^81720418 is an apocalyptic number.

81720418 is a deficient number, since it is larger than the sum of its proper divisors (50468702).

81720418 is a wasteful number, since it uses less digits than its factorization.

81720418 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4281.

The product of its (nonzero) digits is 3584, while the sum is 31.

The square root of 81720418 is about 9039.9346236574. The cubic root of 81720418 is about 433.9538307332.

The spelling of 81720418 in words is "eighty-one million, seven hundred twenty thousand, four hundred eighteen".