20721220 has 24 divisors (see below), whose sum is σ = 46862424. Its totient is φ = 7650816.

The previous prime is 20721209. The next prime is 20721223. The reversal of 20721220 is 2212702.

It can be written as a sum of positive squares in 4 ways, for example, as 145924 + 20575296 = 382^2 + 4536^2 .

It is a junction number, because it is equal to n+sod(n) for n = 20721194 and 20721203.

It is not an unprimeable number, because it can be changed into a prime (20721223) 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 7 ways as a sum of consecutive naturals, for example, 39589 + ... + 40108.

It is an arithmetic number, because the mean of its divisors is an integer number (1952601).

Almost surely, 2^20721220 is an apocalyptic number.

20721220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20721220 is an abundant number, since it is smaller than the sum of its proper divisors (26141204).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20721220 is a wasteful number, since it uses less digits than its factorization.

20721220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 79719 (or 79717 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 16.

The square root of 20721220 is about 4552.0566780303. The cubic root of 20721220 is about 274.6661292550. Note that the first 3 decimals are identical.

Adding to 20721220 its reverse (2212702), we get a palindrome (22933922).

The spelling of 20721220 in words is "twenty million, seven hundred twenty-one thousand, two hundred twenty".