28129991 has 2 divisors, whose sum is σ = 28129992. Its totient is φ = 28129990.

The previous prime is 28129939. The next prime is 28129993. The reversal of 28129991 is 19992182.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 28129991 - 2¹⁰ = 28128967 is a prime.

Together with 28129993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (28129993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 14064995 + 14064996.

It is an arithmetic number, because the mean of its divisors is an integer number (14064996).

Almost surely, 2^28129991 is an apocalyptic number.

28129991 is a deficient number, since it is larger than the sum of its proper divisors (1).

28129991 is an equidigital number, since it uses as much as digits as its factorization.

28129991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23328, while the sum is 41.

The square root of 28129991 is about 5303.7713940177. The cubic root of 28129991 is about 304.1280876155.

The spelling of 28129991 in words is "twenty-eight million, one hundred twenty-nine thousand, nine hundred ninety-one".