21722861 has 2 divisors, whose sum is σ = 21722862. Its totient is φ = 21722860.

The previous prime is 21722851. The next prime is 21722863. The reversal of 21722861 is 16822712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12075625 + 9647236 = 3475^2 + 3106^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21722861 is a prime.

Together with 21722863, 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 (21722863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10861430 + 10861431.

It is an arithmetic number, because the mean of its divisors is an integer number (10861431).

Almost surely, 2^21722861 is an apocalyptic number.

It is an amenable number.

21722861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21722861 is an equidigital number, since it uses as much as digits as its factorization.

21722861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2688, while the sum is 29.

The square root of 21722861 is about 4660.7790121395. The cubic root of 21722861 is about 279.0223600310.

The spelling of 21722861 in words is "twenty-one million, seven hundred twenty-two thousand, eight hundred sixty-one".