21561851 has 2 divisors, whose sum is σ = 21561852. Its totient is φ = 21561850.

The previous prime is 21561817. The next prime is 21561887. The reversal of 21561851 is 15816512.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21561851 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21561251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10780925 + 10780926.

It is an arithmetic number, because the mean of its divisors is an integer number (10780926).

Almost surely, 2^21561851 is an apocalyptic number.

21561851 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561851 is an equidigital number, since it uses as much as digits as its factorization.

21561851 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2400, while the sum is 29.

The square root of 21561851 is about 4643.4740227549. The cubic root of 21561851 is about 278.3312778682.

The spelling of 21561851 in words is "twenty-one million, five hundred sixty-one thousand, eight hundred fifty-one".