7728421 has 16 divisors (see below), whose sum is σ = 8760960. Its totient is φ = 6773760.

The previous prime is 7728403. The next prime is 7728439. The reversal of 7728421 is 1248277.

7728421 = 364² + 365² + ... + 414².

It is an interprime number because it is at equal distance from previous prime (7728403) and next prime (7728439).

It is a 5-Lehmer number, since φ(7728421) divides (7728421-1)⁵.

It is a cyclic number.

It is not a de Polignac number, because 7728421 - 2⁵ = 7728389 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7728401) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 22765 + ... + 23101.

It is an arithmetic number, because the mean of its divisors is an integer number (547560).

Almost surely, 2^7728421 is an apocalyptic number.

7728421 is a gapful number since it is divisible by the number (71) formed by its first and last digit.

It is an amenable number.

7728421 is a deficient number, since it is larger than the sum of its proper divisors (1032539).

7728421 is a wasteful number, since it uses less digits than its factorization.

7728421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 444.

The product of its digits is 6272, while the sum is 31.

The square root of 7728421 is about 2780.0037769759. The cubic root of 7728421 is about 197.7107380433.

The spelling of 7728421 in words is "seven million, seven hundred twenty-eight thousand, four hundred twenty-one".