20491591 has 2 divisors, whose sum is σ = 20491592. Its totient is φ = 20491590.

The previous prime is 20491571. The next prime is 20491609. The reversal of 20491591 is 19519402.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20491591 - 2¹⁹ = 19967303 is a prime.

It is a super-2 number, since 2×20491591² = 839810603422562, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20491561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10245795 + 10245796.

It is an arithmetic number, because the mean of its divisors is an integer number (10245796).

Almost surely, 2^20491591 is an apocalyptic number.

20491591 is a deficient number, since it is larger than the sum of its proper divisors (1).

20491591 is an equidigital number, since it uses as much as digits as its factorization.

20491591 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3240, while the sum is 31.

The square root of 20491591 is about 4526.7638551177. The cubic root of 20491591 is about 273.6477571796.

The spelling of 20491591 in words is "twenty million, four hundred ninety-one thousand, five hundred ninety-one".