20984557 has 4 divisors (see below), whose sum is σ = 22892256. Its totient is φ = 19076860.

The previous prime is 20984503. The next prime is 20984581. The reversal of 20984557 is 75548902.

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.

It is not a de Polignac number, because 20984557 - 2²³ = 12595949 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20984357) 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, 953833 + ... + 953854.

It is an arithmetic number, because the mean of its divisors is an integer number (5723064).

Almost surely, 2^20984557 is an apocalyptic number.

It is an amenable number.

20984557 is a deficient number, since it is larger than the sum of its proper divisors (1907699).

20984557 is a wasteful number, since it uses less digits than its factorization.

20984557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1907698.

The product of its (nonzero) digits is 100800, while the sum is 40.

The square root of 20984557 is about 4580.8904156288. The cubic root of 20984557 is about 275.8247723774.

It can be divided in two parts, 209845 and 57, that added together give a palindrome (209902).

The spelling of 20984557 in words is "twenty million, nine hundred eighty-four thousand, five hundred fifty-seven".