21501251 has 4 divisors (see below), whose sum is σ = 22436112. Its totient is φ = 20566392.

The previous prime is 21501241. The next prime is 21501253. The reversal of 21501251 is 15210512.

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

It is a cyclic number.

It is not a de Polignac number, because 21501251 - 2⁶ = 21501187 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21501253) 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, 467396 + ... + 467441.

It is an arithmetic number, because the mean of its divisors is an integer number (5609028).

Almost surely, 2^21501251 is an apocalyptic number.

21501251 is a deficient number, since it is larger than the sum of its proper divisors (934861).

21501251 is an equidigital number, since it uses as much as digits as its factorization.

21501251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 934860.

The product of its (nonzero) digits is 100, while the sum is 17.

The square root of 21501251 is about 4636.9441445849. The cubic root of 21501251 is about 278.0702813870.

Adding to 21501251 its reverse (15210512), we get a palindrome (36711763).

The spelling of 21501251 in words is "twenty-one million, five hundred one thousand, two hundred fifty-one".