81723778 has 4 divisors (see below), whose sum is σ = 122585670. Its totient is φ = 40861888.

The previous prime is 81723773. The next prime is 81723797. The reversal of 81723778 is 87732718.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 41692849 + 40030929 = 6457^2 + 6327^2 .

It is not an unprimeable number, because it can be changed into a prime (81723773) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20430943 + ... + 20430946.

Almost surely, 2^81723778 is an apocalyptic number.

81723778 is a deficient number, since it is larger than the sum of its proper divisors (40861892).

81723778 is a wasteful number, since it uses less digits than its factorization.

81723778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40861891.

The product of its digits is 131712, while the sum is 43.

The square root of 81723778 is about 9040.1204637991. The cubic root of 81723778 is about 433.9597781040.

The spelling of 81723778 in words is "eighty-one million, seven hundred twenty-three thousand, seven hundred seventy-eight".