81721466 has 4 divisors (see below), whose sum is σ = 122582202. Its totient is φ = 40860732.

The previous prime is 81721439. The next prime is 81721469. The reversal of 81721466 is 66412718.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 66412718 = 2 ⋅33206359.

It can be written as a sum of positive squares in only one way, i.e., 54982225 + 26739241 = 7415^2 + 5171^2 .

It is not an unprimeable number, because it can be changed into a prime (81721469) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20430365 + ... + 20430368.

Almost surely, 2^81721466 is an apocalyptic number.

81721466 is a deficient number, since it is larger than the sum of its proper divisors (40860736).

81721466 is a wasteful number, since it uses less digits than its factorization.

81721466 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40860735.

The product of its digits is 16128, while the sum is 35.

The square root of 81721466 is about 9039.9925884925. The cubic root of 81721466 is about 433.9556857640.

The spelling of 81721466 in words is "eighty-one million, seven hundred twenty-one thousand, four hundred sixty-six".