20991317 has 2 divisors, whose sum is σ = 20991318. Its totient is φ = 20991316.

The previous prime is 20991293. The next prime is 20991319. The reversal of 20991317 is 71319902.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15673681 + 5317636 = 3959^2 + 2306^2 .

It is a cyclic number.

It is not a de Polignac number, because 20991317 - 2¹⁶ = 20925781 is a prime.

Together with 20991319, 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 (20991319) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495658 + 10495659.

It is an arithmetic number, because the mean of its divisors is an integer number (10495659).

Almost surely, 2^20991317 is an apocalyptic number.

It is an amenable number.

20991317 is a deficient number, since it is larger than the sum of its proper divisors (1).

20991317 is an equidigital number, since it uses as much as digits as its factorization.

20991317 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3402, while the sum is 32.

The square root of 20991317 is about 4581.6282040340. The cubic root of 20991317 is about 275.8543874142.

The spelling of 20991317 in words is "twenty million, nine hundred ninety-one thousand, three hundred seventeen".