20891491 has 4 divisors (see below), whose sum is σ = 20983752. Its totient is φ = 20799232.

The previous prime is 20891473. The next prime is 20891503. The reversal of 20891491 is 19419802.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19419802 = 2 ⋅9709901.

It is a cyclic number.

It is not a de Polignac number, because 20891491 - 2⁵ = 20891459 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20891401) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 45790 + ... + 46243.

It is an arithmetic number, because the mean of its divisors is an integer number (5245938).

Almost surely, 2^20891491 is an apocalyptic number.

20891491 is a deficient number, since it is larger than the sum of its proper divisors (92261).

20891491 is an equidigital number, since it uses as much as digits as its factorization.

20891491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92260.

The product of its (nonzero) digits is 5184, while the sum is 34.

The square root of 20891491 is about 4570.7210590890. The cubic root of 20891491 is about 275.4164093685.

The spelling of 20891491 in words is "twenty million, eight hundred ninety-one thousand, four hundred ninety-one".