81721778145 has 16 divisors (see below), whose sum is σ = 149434108800. Its totient is φ = 37358527104.

The previous prime is 81721778137. The next prime is 81721778207. The reversal of 81721778145 is 54187712718.

It is not a de Polignac number, because 81721778145 - 2³ = 81721778137 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 389151220 + ... + 389151429.

It is an arithmetic number, because the mean of its divisors is an integer number (9339631800).

Almost surely, 2^81721778145 is an apocalyptic number.

It is an amenable number.

81721778145 is a deficient number, since it is larger than the sum of its proper divisors (67712330655).

81721778145 is a wasteful number, since it uses less digits than its factorization.

81721778145 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 778302664.

The product of its digits is 878080, while the sum is 51.

The spelling of 81721778145 in words is "eighty-one billion, seven hundred twenty-one million, seven hundred seventy-eight thousand, one hundred forty-five".