20013991 has 2 divisors, whose sum is σ = 20013992. Its totient is φ = 20013990.

The previous prime is 20013971. The next prime is 20013997. The reversal of 20013991 is 19931002.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20013991 - 2¹⁵ = 19981223 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20013997) 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, 10006995 + 10006996.

It is an arithmetic number, because the mean of its divisors is an integer number (10006996).

Almost surely, 2^20013991 is an apocalyptic number.

20013991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20013991 is an equidigital number, since it uses as much as digits as its factorization.

20013991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 486, while the sum is 25.

The square root of 20013991 is about 4473.6999228826. The cubic root of 20013991 is about 271.5050426005.

Adding to 20013991 its reverse (19931002), we get a palindrome (39944993).

The spelling of 20013991 in words is "twenty million, thirteen thousand, nine hundred ninety-one".