21857651 has 2 divisors, whose sum is σ = 21857652. Its totient is φ = 21857650.

The previous prime is 21857621. The next prime is 21857653. The reversal of 21857651 is 15675812.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21857651 is a prime.

Together with 21857653, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21857653) by changing a digit.

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 as a sum of consecutive naturals, namely, 10928825 + 10928826.

It is an arithmetic number, because the mean of its divisors is an integer number (10928826).

Almost surely, 2^21857651 is an apocalyptic number.

21857651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21857651 is an equidigital number, since it uses as much as digits as its factorization.

21857651 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16800, while the sum is 35.

The square root of 21857651 is about 4675.2166794706. The cubic root of 21857651 is about 279.5982802153.

The spelling of 21857651 in words is "twenty-one million, eight hundred fifty-seven thousand, six hundred fifty-one".