20508991 has 2 divisors, whose sum is σ = 20508992. Its totient is φ = 20508990.

The previous prime is 20508941. The next prime is 20508997. The reversal of 20508991 is 19980502.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20508991 - 2¹¹ = 20506943 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20508997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10254495 + 10254496.

It is an arithmetic number, because the mean of its divisors is an integer number (10254496).

Almost surely, 2^20508991 is an apocalyptic number.

20508991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20508991 is an equidigital number, since it uses as much as digits as its factorization.

20508991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6480, while the sum is 34.

The square root of 20508991 is about 4528.6853500768. The cubic root of 20508991 is about 273.7251893307.

The spelling of 20508991 in words is "twenty million, five hundred eight thousand, nine hundred ninety-one".