20721247 has 4 divisors (see below), whose sum is σ = 20954160. Its totient is φ = 20488336.

The previous prime is 20721223. The next prime is 20721263. The reversal of 20721247 is 74212702.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20721247 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20721287) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 116323 + ... + 116500.

It is an arithmetic number, because the mean of its divisors is an integer number (5238540).

Almost surely, 2^20721247 is an apocalyptic number.

20721247 is a deficient number, since it is larger than the sum of its proper divisors (232913).

20721247 is an equidigital number, since it uses as much as digits as its factorization.

20721247 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 232912.

The product of its (nonzero) digits is 1568, while the sum is 25.

The square root of 20721247 is about 4552.0596437217. The cubic root of 20721247 is about 274.6662485527. Note that the first 3 decimals are identical.

Adding to 20721247 its reverse (74212702), we get a palindrome (94933949).

The spelling of 20721247 in words is "twenty million, seven hundred twenty-one thousand, two hundred forty-seven".