28756421 has 4 divisors (see below), whose sum is σ = 28905612. Its totient is φ = 28607232.

The previous prime is 28756391. The next prime is 28756447. The reversal of 28756421 is 12465782.

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

It can be written as a sum of positive squares in 2 ways, for example, as 21390625 + 7365796 = 4625^2 + 2714^2 .

It is not a de Polignac number, because 28756421 - 2¹⁴ = 28740037 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 (28756451) 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, 74306 + ... + 74691.

It is an arithmetic number, because the mean of its divisors is an integer number (7226403).

It is the magic constant of a 386 × 386 magic square.

Almost surely, 2^28756421 is an apocalyptic number.

It is an amenable number.

28756421 is a deficient number, since it is larger than the sum of its proper divisors (149191).

28756421 is a wasteful number, since it uses less digits than its factorization.

28756421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 149190.

The product of its digits is 26880, while the sum is 35.

The square root of 28756421 is about 5362.5013752912. The cubic root of 28756421 is about 306.3690884347.

The spelling of 28756421 in words is "twenty-eight million, seven hundred fifty-six thousand, four hundred twenty-one".