81799972 has 6 divisors (see below), whose sum is σ = 143149958. Its totient is φ = 40899984.

The previous prime is 81799897. The next prime is 81799973. The reversal of 81799972 is 27999718.

It can be written as a sum of positive squares in only one way, i.e., 53348416 + 28451556 = 7304^2 + 5334^2 .

It is not an unprimeable number, because it can be changed into a prime (81799973) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10224993 + ... + 10225000.

Almost surely, 2^81799972 is an apocalyptic number.

It is an amenable number.

81799972 is a deficient number, since it is larger than the sum of its proper divisors (61349986).

81799972 is a wasteful number, since it uses less digits than its factorization.

81799972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20449997 (or 20449995 counting only the distinct ones).

The product of its digits is 571536, while the sum is 52.

The square root of 81799972 is about 9044.3336957456. Note that the first 3 decimals coincide. The cubic root of 81799972 is about 434.0946016178.

The spelling of 81799972 in words is "eighty-one million, seven hundred ninety-nine thousand, nine hundred seventy-two".