20721065 has 8 divisors (see below), whose sum is σ = 24975240. Its totient is φ = 16503552.

The previous prime is 20721053. The next prime is 20721083. The reversal of 20721065 is 56012702.

It can be written as a sum of positive squares in 4 ways, for example, as 2768896 + 17952169 = 1664^2 + 4237^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 20721065 - 2¹⁶ = 20655529 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20721065.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7904 + ... + 10193.

It is an arithmetic number, because the mean of its divisors is an integer number (3121905).

Almost surely, 2^20721065 is an apocalyptic number.

It is an amenable number.

20721065 is a deficient number, since it is larger than the sum of its proper divisors (4254175).

20721065 is a wasteful number, since it uses less digits than its factorization.

20721065 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18331.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 20721065 is about 4552.0396527271. The cubic root of 20721065 is about 274.6654443958.

Adding to 20721065 its reverse (56012702), we get a palindrome (76733767).

The spelling of 20721065 in words is "twenty million, seven hundred twenty-one thousand, sixty-five".