20721213 has 12 divisors (see below), whose sum is σ = 30438720. Its totient is φ = 13579656.

The previous prime is 20721209. The next prime is 20721223. The reversal of 20721213 is 31212702.

It is not a de Polignac number, because 20721213 - 2² = 20721209 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721223) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18981 + ... + 20042.

It is an arithmetic number, because the mean of its divisors is an integer number (2536560).

Almost surely, 2^20721213 is an apocalyptic number.

It is an amenable number.

20721213 is a deficient number, since it is larger than the sum of its proper divisors (9717507).

20721213 is a wasteful number, since it uses less digits than its factorization.

20721213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39088 (or 39085 counting only the distinct ones).

The product of its (nonzero) digits is 168, while the sum is 18.

The square root of 20721213 is about 4552.0559091470. The cubic root of 20721213 is about 274.6660983260. Note that the first 3 decimals are identical.

Adding to 20721213 its reverse (31212702), we get a palindrome (51933915).

The spelling of 20721213 in words is "twenty million, seven hundred twenty-one thousand, two hundred thirteen".