21956861 has 2 divisors, whose sum is σ = 21956862. Its totient is φ = 21956860.

The previous prime is 21956839. The next prime is 21956863. The reversal of 21956861 is 16865912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19412836 + 2544025 = 4406^2 + 1595^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21956861 is a prime.

Together with 21956863, 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 (21956863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10978430 + 10978431.

It is an arithmetic number, because the mean of its divisors is an integer number (10978431).

Almost surely, 2^21956861 is an apocalyptic number.

It is an amenable number.

21956861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21956861 is an equidigital number, since it uses as much as digits as its factorization.

21956861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25920, while the sum is 38.

The square root of 21956861 is about 4685.8148704361. The cubic root of 21956861 is about 280.0206659917.

The spelling of 21956861 in words is "twenty-one million, nine hundred fifty-six thousand, eight hundred sixty-one".