8181721 has 8 divisors (see below), whose sum is σ = 8607744. Its totient is φ = 7761600.

The previous prime is 8181697. The next prime is 8181727. The reversal of 8181721 is 1271818.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-8181721 is a prime.

It is a Duffinian number.

8181721 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 8181721.

It is not an unprimeable number, because it can be changed into a prime (8181727) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1521 + ... + 4321.

It is an arithmetic number, because the mean of its divisors is an integer number (1075968).

Almost surely, 2^8181721 is an apocalyptic number.

It is an amenable number.

8181721 is a deficient number, since it is larger than the sum of its proper divisors (426023).

8181721 is a wasteful number, since it uses less digits than its factorization.

8181721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2951.

The product of its digits is 896, while the sum is 28.

The square root of 8181721 is about 2860.3707801612. The cubic root of 8181721 is about 201.5030180552.

Subtracting from 8181721 its reverse (1271818), we obtain a triangular number (6909903 = T₃₇₁₇).

The spelling of 8181721 in words is "eight million, one hundred eighty-one thousand, seven hundred twenty-one".