81721011 has 4 divisors (see below), whose sum is σ = 108961352. Its totient is φ = 54480672.

The previous prime is 81720973. The next prime is 81721021. The reversal of 81721011 is 11012718.

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

It is not a de Polignac number, because 81721011 - 2⁷ = 81720883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81721021) 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, 13620166 + ... + 13620171.

It is an arithmetic number, because the mean of its divisors is an integer number (27240338).

Almost surely, 2^81721011 is an apocalyptic number.

81721011 is a deficient number, since it is larger than the sum of its proper divisors (27240341).

81721011 is a wasteful number, since it uses less digits than its factorization.

81721011 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27240340.

The product of its (nonzero) digits is 112, while the sum is 21.

The square root of 81721011 is about 9039.9674225077. The cubic root of 81721011 is about 433.9548803852.

Adding to 81721011 its reverse (11012718), we get a palindrome (92733729).

The spelling of 81721011 in words is "eighty-one million, seven hundred twenty-one thousand, eleven".