20991393 has 20 divisors (see below), whose sum is σ = 31491460. Its totient is φ = 13934592.

The previous prime is 20991361. The next prime is 20991401. The reversal of 20991393 is 39319902.

It can be written as a sum of positive squares in 2 ways, for example, as 6906384 + 14085009 = 2628^2 + 3753^2 .

It is not a de Polignac number, because 20991393 - 2⁵ = 20991361 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991323) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 26913 + ... + 27681.

It is an arithmetic number, because the mean of its divisors is an integer number (1574573).

Almost surely, 2^20991393 is an apocalyptic number.

It is an amenable number.

20991393 is a deficient number, since it is larger than the sum of its proper divisors (10500067).

20991393 is an equidigital number, since it uses as much as digits as its factorization.

20991393 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1118 (or 1109 counting only the distinct ones).

The product of its (nonzero) digits is 13122, while the sum is 36.

The square root of 20991393 is about 4581.6364980212. The cubic root of 20991393 is about 275.8547203281.

The spelling of 20991393 in words is "twenty million, nine hundred ninety-one thousand, three hundred ninety-three".