8721421 has 4 divisors (see below), whose sum is σ = 8730432. Its totient is φ = 8712412.

The previous prime is 8721413. The next prime is 8721443. The reversal of 8721421 is 1241278.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 1241278 = 2 ⋅620639.

It is a cyclic number.

It is not a de Polignac number, because 8721421 - 2³ = 8721413 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (8721481) 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, 2851 + ... + 5056.

It is an arithmetic number, because the mean of its divisors is an integer number (2182608).

Almost surely, 2^8721421 is an apocalyptic number.

It is an amenable number.

8721421 is a deficient number, since it is larger than the sum of its proper divisors (9011).

8721421 is a wasteful number, since it uses less digits than its factorization.

8721421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9010.

The product of its digits is 896, while the sum is 25.

The square root of 8721421 is about 2953.2052079055. The cubic root of 8721421 is about 205.8396732227.

Adding to 8721421 its reverse (1241278), we get a palindrome (9962699).

The spelling of 8721421 in words is "eight million, seven hundred twenty-one thousand, four hundred twenty-one".