81721572628 has 12 divisors (see below), whose sum is σ = 143075028852. Its totient is φ = 40842992960.

The previous prime is 81721572617. The next prime is 81721572629. The reversal of 81721572628 is 82627512718.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 45489211524 + 36232361104 = 213282^2 + 190348^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81721572629) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4438003 + ... + 4456378.

It is an arithmetic number, because the mean of its divisors is an integer number (11922919071).

Almost surely, 2^81721572628 is an apocalyptic number.

It is an amenable number.

81721572628 is a deficient number, since it is larger than the sum of its proper divisors (61353456224).

81721572628 is a wasteful number, since it uses less digits than its factorization.

81721572628 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8896682 (or 8896680 counting only the distinct ones).

The product of its digits is 752640, while the sum is 49.

The spelling of 81721572628 in words is "eighty-one billion, seven hundred twenty-one million, five hundred seventy-two thousand, six hundred twenty-eight".