21856139 has 2 divisors, whose sum is σ = 21856140. Its totient is φ = 21856138.

The previous prime is 21856129. The next prime is 21856151. The reversal of 21856139 is 93165812.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21856139 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21856099 and 21856108.

It is not a weakly prime, because it can be changed into another prime (21856129) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10928069 + 10928070.

It is an arithmetic number, because the mean of its divisors is an integer number (10928070).

Almost surely, 2^21856139 is an apocalyptic number.

21856139 is a deficient number, since it is larger than the sum of its proper divisors (1).

21856139 is an equidigital number, since it uses as much as digits as its factorization.

21856139 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12960, while the sum is 35.

The square root of 21856139 is about 4675.0549729388. The cubic root of 21856139 is about 279.5918330092.

The spelling of 21856139 in words is "twenty-one million, eight hundred fifty-six thousand, one hundred thirty-nine".