21885781 has 2 divisors, whose sum is σ = 21885782. Its totient is φ = 21885780.

The previous prime is 21885779. The next prime is 21885797. The reversal of 21885781 is 18758812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18879025 + 3006756 = 4345^2 + 1734^2 .

It is a cyclic number.

It is not a de Polignac number, because 21885781 - 2¹ = 21885779 is a prime.

It is a super-2 number, since 2×21885781² = 957974819959922, which contains 22 as substring.

Together with 21885779, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21885881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10942890 + 10942891.

It is an arithmetic number, because the mean of its divisors is an integer number (10942891).

Almost surely, 2^21885781 is an apocalyptic number.

It is an amenable number.

21885781 is a deficient number, since it is larger than the sum of its proper divisors (1).

21885781 is an equidigital number, since it uses as much as digits as its factorization.

21885781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 35840, while the sum is 40.

The square root of 21885781 is about 4678.2241288763. The cubic root of 21885781 is about 279.7181730620.

The spelling of 21885781 in words is "twenty-one million, eight hundred eighty-five thousand, seven hundred eighty-one".