21857779 has 2 divisors, whose sum is σ = 21857780. Its totient is φ = 21857778.

The previous prime is 21857753. The next prime is 21857807. The reversal of 21857779 is 97775812.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21857779 - 2⁵ = 21857747 is a prime.

It is not a weakly prime, because it can be changed into another prime (21857749) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10928889 + 10928890.

It is an arithmetic number, because the mean of its divisors is an integer number (10928890).

Almost surely, 2^21857779 is an apocalyptic number.

21857779 is a deficient number, since it is larger than the sum of its proper divisors (1).

21857779 is an equidigital number, since it uses as much as digits as its factorization.

21857779 is an evil number, because the sum of its binary digits is even.

The product of its digits is 246960, while the sum is 46.

The square root of 21857779 is about 4675.2303686556. The cubic root of 21857779 is about 279.5988259969.

The spelling of 21857779 in words is "twenty-one million, eight hundred fifty-seven thousand, seven hundred seventy-nine".