20845621 has 4 divisors (see below), whose sum is σ = 22071852. Its totient is φ = 19619392.

The previous prime is 20845579. The next prime is 20845631. The reversal of 20845621 is 12654802.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12654802 = 2 ⋅6327401.

It can be written as a sum of positive squares in 2 ways, for example, as 18610596 + 2235025 = 4314^2 + 1495^2 .

It is a cyclic number.

It is not a de Polignac number, because 20845621 - 2¹³ = 20837429 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20845621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20845631) 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, 613090 + ... + 613123.

It is an arithmetic number, because the mean of its divisors is an integer number (5517963).

Almost surely, 2^20845621 is an apocalyptic number.

It is an amenable number.

20845621 is a deficient number, since it is larger than the sum of its proper divisors (1226231).

20845621 is a wasteful number, since it uses less digits than its factorization.

20845621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1226230.

The product of its (nonzero) digits is 3840, while the sum is 28.

The square root of 20845621 is about 4565.7004939001. The cubic root of 20845621 is about 275.2146907509.

The spelling of 20845621 in words is "twenty million, eight hundred forty-five thousand, six hundred twenty-one".