20993281 has 2 divisors, whose sum is σ = 20993282. Its totient is φ = 20993280.

The previous prime is 20993279. The next prime is 20993339. The reversal of 20993281 is 18239902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18352656 + 2640625 = 4284^2 + 1625^2 .

It is a cyclic number.

It is not a de Polignac number, because 20993281 - 2¹ = 20993279 is a prime.

It is a super-2 number, since 2×20993281² = 881435694289922, which contains 22 as substring.

Together with 20993279, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (20993201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10496640 + 10496641.

It is an arithmetic number, because the mean of its divisors is an integer number (10496641).

Almost surely, 2^20993281 is an apocalyptic number.

It is an amenable number.

20993281 is a deficient number, since it is larger than the sum of its proper divisors (1).

20993281 is an equidigital number, since it uses as much as digits as its factorization.

20993281 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7776, while the sum is 34.

The square root of 20993281 is about 4581.8425333047. The cubic root of 20993281 is about 275.8629903541.

The spelling of 20993281 in words is "twenty million, nine hundred ninety-three thousand, two hundred eighty-one".