20721243 has 8 divisors (see below), whose sum is σ = 27651856. Its totient is φ = 13802400.

The previous prime is 20721223. The next prime is 20721263. The reversal of 20721243 is 34212702.

It is an interprime number because it is at equal distance from previous prime (20721223) and next prime (20721263).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 20721243 - 2⁹ = 20720731 is a prime.

It is a super-2 number, since 2×20721243² = 858739822930098, which contains 22 as substring.

It is a Duffinian 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 7 ways as a sum of consecutive naturals, for example, 2733 + ... + 6993.

It is an arithmetic number, because the mean of its divisors is an integer number (3456482).

Almost surely, 2^20721243 is an apocalyptic number.

20721243 is a deficient number, since it is larger than the sum of its proper divisors (6930613).

20721243 is a wasteful number, since it uses less digits than its factorization.

20721243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5885.

The product of its (nonzero) digits is 672, while the sum is 21.

The square root of 20721243 is about 4552.0592043602. The cubic root of 20721243 is about 274.6662308790. Note that the first 3 decimals are identical.

Adding to 20721243 its reverse (34212702), we get a palindrome (54933945).

The spelling of 20721243 in words is "twenty million, seven hundred twenty-one thousand, two hundred forty-three".