21839561 has 2 divisors, whose sum is σ = 21839562. Its totient is φ = 21839560.

The previous prime is 21839557. The next prime is 21839563. The reversal of 21839561 is 16593812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21799561 + 40000 = 4669^2 + 200^2 .

It is a cyclic number.

It is not a de Polignac number, because 21839561 - 2² = 21839557 is a prime.

It is a Sophie Germain prime.

Together with 21839563, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21839563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10919780 + 10919781.

It is an arithmetic number, because the mean of its divisors is an integer number (10919781).

Almost surely, 2^21839561 is an apocalyptic number.

It is an amenable number.

21839561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21839561 is an equidigital number, since it uses as much as digits as its factorization.

21839561 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 21839561 is about 4673.2816093191. The cubic root of 21839561 is about 279.5211244878.

The spelling of 21839561 in words is "twenty-one million, eight hundred thirty-nine thousand, five hundred sixty-one".