20553991 has 4 divisors (see below), whose sum is σ = 21635800. Its totient is φ = 19472184.

The previous prime is 20553989. The next prime is 20554013. The reversal of 20553991 is 19935502.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 20553991 - 2¹ = 20553989 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 (20553931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 540876 + ... + 540913.

It is an arithmetic number, because the mean of its divisors is an integer number (5408950).

Almost surely, 2^20553991 is an apocalyptic number.

20553991 is a deficient number, since it is larger than the sum of its proper divisors (1081809).

20553991 is a wasteful number, since it uses less digits than its factorization.

20553991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1081808.

The product of its (nonzero) digits is 12150, while the sum is 34.

The square root of 20553991 is about 4533.6509570103. The cubic root of 20553991 is about 273.9252420057.

The spelling of 20553991 in words is "twenty million, five hundred fifty-three thousand, nine hundred ninety-one".