20721284 has 6 divisors (see below), whose sum is σ = 36262254. Its totient is φ = 10360640.

The previous prime is 20721271. The next prime is 20721287. The reversal of 20721284 is 48212702.

It can be written as a sum of positive squares in only one way, i.e., 19998784 + 722500 = 4472^2 + 850^2 .

It is a super-2 number, since 2×20721284² = 858743221217312, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (20721287) 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 as a sum of consecutive naturals, namely, 2590157 + ... + 2590164.

It is an arithmetic number, because the mean of its divisors is an integer number (6043709).

Almost surely, 2^20721284 is an apocalyptic number.

It is an amenable number.

20721284 is a deficient number, since it is larger than the sum of its proper divisors (15540970).

20721284 is a wasteful number, since it uses less digits than its factorization.

20721284 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5180325 (or 5180323 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 20721284 is about 4552.0637078143. The cubic root of 20721284 is about 274.6664120346. Note that the first 3 decimals are identical.

Adding to 20721284 its reverse (48212702), we get a palindrome (68933986).

The spelling of 20721284 in words is "twenty million, seven hundred twenty-one thousand, two hundred eighty-four".