20556221 has 4 divisors (see below), whose sum is σ = 23492832. Its totient is φ = 17619612.

The previous prime is 20556199. The next prime is 20556223. The reversal of 20556221 is 12265502.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12265502 = 2 ⋅6132751.

It is a cyclic number.

It is not a de Polignac number, because 20556221 - 2¹⁸ = 20294077 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 (20556223) 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, 1468295 + ... + 1468308.

It is an arithmetic number, because the mean of its divisors is an integer number (5873208).

Almost surely, 2^20556221 is an apocalyptic number.

It is an amenable number.

20556221 is a deficient number, since it is larger than the sum of its proper divisors (2936611).

20556221 is an equidigital number, since it uses as much as digits as its factorization.

20556221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2936610.

The product of its (nonzero) digits is 1200, while the sum is 23.

The square root of 20556221 is about 4533.8968889907. The cubic root of 20556221 is about 273.9351481305.

The spelling of 20556221 in words is "twenty million, five hundred fifty-six thousand, two hundred twenty-one".