21811861 has 2 divisors, whose sum is σ = 21811862. Its totient is φ = 21811860.

The previous prime is 21811849. The next prime is 21811873. The reversal of 21811861 is 16811812.

It is a balanced prime because it is at equal distance from previous prime (21811849) and next prime (21811873).

It can be written as a sum of positive squares in only one way, i.e., 14554225 + 7257636 = 3815^2 + 2694^2 .

It is a cyclic number.

It is not a de Polignac number, because 21811861 - 2⁷ = 21811733 is a prime.

It is a Chen prime.

It is equal to p_1378072 and since 21811861 and 1378072 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21811891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10905930 + 10905931.

It is an arithmetic number, because the mean of its divisors is an integer number (10905931).

Almost surely, 2^21811861 is an apocalyptic number.

It is an amenable number.

21811861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21811861 is an equidigital number, since it uses as much as digits as its factorization.

21811861 is an evil number, because the sum of its binary digits is even.

The product of its digits is 768, while the sum is 28.

The square root of 21811861 is about 4670.3170127947. The cubic root of 21811861 is about 279.4028985013.

The spelling of 21811861 in words is "twenty-one million, eight hundred eleven thousand, eight hundred sixty-one".