8415721 has 4 divisors (see below), whose sum is σ = 8421700. Its totient is φ = 8409744.

The previous prime is 8415709. The next prime is 8415733. The reversal of 8415721 is 1275148.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (8415709) and next prime (8415733).

It can be written as a sum of positive squares in 2 ways, for example, as 1125721 + 7290000 = 1061^2 + 2700^2 .

It is a cyclic number.

It is not a de Polignac number, because 8415721 - 2¹⁵ = 8382953 is a prime.

It is a Duffinian number.

8415721 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 8415721.

It is not an unprimeable number, because it can be changed into a prime (8413721) 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, 415 + ... + 4123.

It is an arithmetic number, because the mean of its divisors is an integer number (2105425).

Almost surely, 2^8415721 is an apocalyptic number.

It is an amenable number.

8415721 is a deficient number, since it is larger than the sum of its proper divisors (5979).

8415721 is a wasteful number, since it uses less digits than its factorization.

8415721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5978.

The product of its digits is 2240, while the sum is 28.

The square root of 8415721 is about 2900.9862116184. The cubic root of 8415721 is about 203.4060079434.

The spelling of 8415721 in words is "eight million, four hundred fifteen thousand, seven hundred twenty-one".