21865981 has 2 divisors, whose sum is σ = 21865982. Its totient is φ = 21865980.

The previous prime is 21865969. The next prime is 21865993. The reversal of 21865981 is 18956812.

It is a balanced prime because it is at equal distance from previous prime (21865969) and next prime (21865993).

It can be written as a sum of positive squares in only one way, i.e., 18198756 + 3667225 = 4266^2 + 1915^2 .

It is a cyclic number.

It is not a de Polignac number, because 21865981 - 2⁹ = 21865469 is a prime.

It is a super-2 number, since 2×21865981² = 956242250184722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21865901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932990 + 10932991.

It is an arithmetic number, because the mean of its divisors is an integer number (10932991).

Almost surely, 2^21865981 is an apocalyptic number.

It is an amenable number.

21865981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21865981 is an equidigital number, since it uses as much as digits as its factorization.

21865981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 34560, while the sum is 40.

The square root of 21865981 is about 4676.1074624093. The cubic root of 21865981 is about 279.6337942156.

The spelling of 21865981 in words is "twenty-one million, eight hundred sixty-five thousand, nine hundred eighty-one".