21578861 has 2 divisors, whose sum is σ = 21578862. Its totient is φ = 21578860.

The previous prime is 21578827. The next prime is 21578863. The reversal of 21578861 is 16887512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16760836 + 4818025 = 4094^2 + 2195^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21578861 is a prime.

Together with 21578863, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21578863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10789430 + 10789431.

It is an arithmetic number, because the mean of its divisors is an integer number (10789431).

Almost surely, 2^21578861 is an apocalyptic number.

It is an amenable number.

21578861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21578861 is an equidigital number, since it uses as much as digits as its factorization.

21578861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 26880, while the sum is 38.

The square root of 21578861 is about 4645.3052644579. The cubic root of 21578861 is about 278.4044498576.

The spelling of 21578861 in words is "twenty-one million, five hundred seventy-eight thousand, eight hundred sixty-one".