20681991 has 48 divisors (see below), whose sum is σ = 35223552. Its totient is φ = 11563200.

The previous prime is 20681957. The next prime is 20681993. The reversal of 20681991 is 19918602.

It is not a de Polignac number, because 20681991 - 2¹⁰ = 20680967 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20681993) 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 in 47 ways as a sum of consecutive naturals, for example, 70441 + ... + 70733.

It is an arithmetic number, because the mean of its divisors is an integer number (733824).

Almost surely, 2^20681991 is an apocalyptic number.

20681991 is a deficient number, since it is larger than the sum of its proper divisors (14541561).

20681991 is a wasteful number, since it uses less digits than its factorization.

20681991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 364 (or 361 counting only the distinct ones).

The product of its (nonzero) digits is 7776, while the sum is 36.

The square root of 20681991 is about 4547.7457052918. The cubic root of 20681991 is about 274.4926889470.

The spelling of 20681991 in words is "twenty million, six hundred eighty-one thousand, nine hundred ninety-one".