28911391 has 4 divisors (see below), whose sum is σ = 30168432. Its totient is φ = 27654352.

The previous prime is 28911359. The next prime is 28911397. The reversal of 28911391 is 19311982.

28911391 = 613² + 614² + ... + 681².

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19311982 = 2 ⋅9655991.

It is a cyclic number.

It is not a de Polignac number, because 28911391 - 2⁵ = 28911359 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 (28911397) 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, 628486 + ... + 628531.

It is an arithmetic number, because the mean of its divisors is an integer number (7542108).

Almost surely, 2^28911391 is an apocalyptic number.

28911391 is a deficient number, since it is larger than the sum of its proper divisors (1257041).

28911391 is a wasteful number, since it uses less digits than its factorization.

28911391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1257040.

The product of its digits is 3888, while the sum is 34.

The square root of 28911391 is about 5376.9313739344. The cubic root of 28911391 is about 306.9184496227.

The spelling of 28911391 in words is "twenty-eight million, nine hundred eleven thousand, three hundred ninety-one".