128497991 has 2 divisors, whose sum is σ = 128497992. Its totient is φ = 128497990.

The previous prime is 128497949. The next prime is 128497997. The reversal of 128497991 is 199794821.

It is a strong prime.

It is an emirp because it is prime and its reverse (199794821) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 128497991 - 2¹⁴ = 128481607 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (128497997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64248995 + 64248996.

It is an arithmetic number, because the mean of its divisors is an integer number (64248996).

Almost surely, 2^128497991 is an apocalyptic number.

128497991 is a deficient number, since it is larger than the sum of its proper divisors (1).

128497991 is an equidigital number, since it uses as much as digits as its factorization.

128497991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 326592, while the sum is 50.

The square root of 128497991 is about 11335.6954352170. The cubic root of 128497991 is about 504.6211464319.

The spelling of 128497991 in words is "one hundred twenty-eight million, four hundred ninety-seven thousand, nine hundred ninety-one".