21955861 has 2 divisors, whose sum is σ = 21955862. Its totient is φ = 21955860.

The previous prime is 21955859. The next prime is 21955867. The reversal of 21955861 is 16855912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21911761 + 44100 = 4681^2 + 210^2 .

It is a cyclic number.

It is not a de Polignac number, because 21955861 - 2¹ = 21955859 is a prime.

Together with 21955859, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21955861.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21955867) 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, 10977930 + 10977931.

It is an arithmetic number, because the mean of its divisors is an integer number (10977931).

Almost surely, 2^21955861 is an apocalyptic number.

It is an amenable number.

21955861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21955861 is an equidigital number, since it uses as much as digits as its factorization.

21955861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 21600, while the sum is 37.

The square root of 21955861 is about 4685.7081641946. The cubic root of 21955861 is about 280.0164148540.

The spelling of 21955861 in words is "twenty-one million, nine hundred fifty-five thousand, eight hundred sixty-one".