20921491 has 4 divisors (see below), whose sum is σ = 21186400. Its totient is φ = 20656584.

The previous prime is 20921479. The next prime is 20921501. The reversal of 20921491 is 19412902.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19412902 = 2 ⋅9706451.

It is a cyclic number.

It is not a de Polignac number, because 20921491 - 2⁷ = 20921363 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20921401) 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, 132336 + ... + 132493.

It is an arithmetic number, because the mean of its divisors is an integer number (5296600).

Almost surely, 2^20921491 is an apocalyptic number.

20921491 is a deficient number, since it is larger than the sum of its proper divisors (264909).

20921491 is an equidigital number, since it uses as much as digits as its factorization.

20921491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 264908.

The product of its (nonzero) digits is 1296, while the sum is 28.

The square root of 20921491 is about 4574.0016397024. The cubic root of 20921491 is about 275.5481781745.

It can be divided in two parts, 20921 and 491, that added together give a palindrome (21412).

The spelling of 20921491 in words is "twenty million, nine hundred twenty-one thousand, four hundred ninety-one".