20998557 has 6 divisors (see below), whose sum is σ = 30331262. Its totient is φ = 13999032.

The previous prime is 20998531. The next prime is 20998583. The reversal of 20998557 is 75589902.

It is a happy number.

20998557 is a `hidden beast` number, since 2 + 0 + 9 + 98 + 557 = 666.

It is an interprime number because it is at equal distance from previous prime (20998531) and next prime (20998583).

It can be written as a sum of positive squares in only one way, i.e., 20985561 + 12996 = 4581^2 + 114^2 .

It is not a de Polignac number, because 20998557 - 2¹⁶ = 20933021 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 (20998157) 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 5 ways as a sum of consecutive naturals, for example, 1166578 + ... + 1166595.

Almost surely, 2^20998557 is an apocalyptic number.

It is an amenable number.

20998557 is a deficient number, since it is larger than the sum of its proper divisors (9332705).

20998557 is a wasteful number, since it uses less digits than its factorization.

20998557 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2333179 (or 2333176 counting only the distinct ones).

The product of its (nonzero) digits is 226800, while the sum is 45.

The square root of 20998557 is about 4582.4182480433. The cubic root of 20998557 is about 275.8860982432.

The spelling of 20998557 in words is "twenty million, nine hundred ninety-eight thousand, five hundred fifty-seven".