20308991 has 2 divisors, whose sum is σ = 20308992. Its totient is φ = 20308990.

The previous prime is 20308969. The next prime is 20308993. The reversal of 20308991 is 19980302.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20308991 is a prime.

Together with 20308993, 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 (20308993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10154495 + 10154496.

It is an arithmetic number, because the mean of its divisors is an integer number (10154496).

Almost surely, 2^20308991 is an apocalyptic number.

20308991 is a deficient number, since it is larger than the sum of its proper divisors (1).

20308991 is an equidigital number, since it uses as much as digits as its factorization.

20308991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 32.

The square root of 20308991 is about 4506.5497889183. The cubic root of 20308991 is about 272.8325082805.

The spelling of 20308991 in words is "twenty million, three hundred eight thousand, nine hundred ninety-one".