21004251 has 16 divisors (see below), whose sum is σ = 28454400. Its totient is φ = 13780800.

The previous prime is 21004241. The next prime is 21004261. The reversal of 21004251 is 15240012.

It is an interprime number because it is at equal distance from previous prime (21004241) and next prime (21004261).

It is not a de Polignac number, because 21004251 - 2¹¹ = 21002203 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21004251.

It is not an unprimeable number, because it can be changed into a prime (21004211) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 90031 + ... + 90263.

It is an arithmetic number, because the mean of its divisors is an integer number (1778400).

Almost surely, 2^21004251 is an apocalyptic number.

21004251 is a deficient number, since it is larger than the sum of its proper divisors (7450149).

21004251 is a wasteful number, since it uses less digits than its factorization.

21004251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 586.

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21004251 is about 4583.0394936112. The cubic root of 21004251 is about 275.9110325514.

Adding to 21004251 its reverse (15240012), we get a palindrome (36244263).

The spelling of 21004251 in words is "twenty-one million, four thousand, two hundred fifty-one".