20921671 has 4 divisors (see below), whose sum is σ = 20982312. Its totient is φ = 20861032.

The previous prime is 20921657. The next prime is 20921689. The reversal of 20921671 is 17612902.

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: 17612902 = 2 ⋅8806451.

It is a cyclic number.

It is not a de Polignac number, because 20921671 - 2¹¹ = 20919623 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 (20921371) 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, 29800 + ... + 30493.

It is an arithmetic number, because the mean of its divisors is an integer number (5245578).

Almost surely, 2^20921671 is an apocalyptic number.

20921671 is a deficient number, since it is larger than the sum of its proper divisors (60641).

20921671 is an equidigital number, since it uses as much as digits as its factorization.

20921671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60640.

The product of its (nonzero) digits is 1512, while the sum is 28.

The square root of 20921671 is about 4574.0213160850. The cubic root of 20921671 is about 275.5489684071.

The spelling of 20921671 in words is "twenty million, nine hundred twenty-one thousand, six hundred seventy-one".