21251651 has 4 divisors (see below), whose sum is σ = 21260904. Its totient is φ = 21242400.

The previous prime is 21251617. The next prime is 21251669. The reversal of 21251651 is 15615212.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21251651 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21251611) 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, 1736 + ... + 6746.

It is an arithmetic number, because the mean of its divisors is an integer number (5315226).

Almost surely, 2^21251651 is an apocalyptic number.

21251651 is a deficient number, since it is larger than the sum of its proper divisors (9253).

21251651 is an equidigital number, since it uses as much as digits as its factorization.

21251651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9252.

The product of its digits is 600, while the sum is 23.

The square root of 21251651 is about 4609.9513012612. The cubic root of 21251651 is about 276.9900859663.

Adding to 21251651 its reverse (15615212), we get a palindrome (36866863).

The spelling of 21251651 in words is "twenty-one million, two hundred fifty-one thousand, six hundred fifty-one".