21706381 has 2 divisors, whose sum is σ = 21706382. Its totient is φ = 21706380.

The previous prime is 21706361. The next prime is 21706387. The reversal of 21706381 is 18360712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21706281 + 100 = 4659^2 + 10^2 .

It is a cyclic number.

It is not a de Polignac number, because 21706381 - 2⁷ = 21706253 is a prime.

It is a super-2 number, since 2×21706381² = 942333952234322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21706387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10853190 + 10853191.

It is an arithmetic number, because the mean of its divisors is an integer number (10853191).

Almost surely, 2^21706381 is an apocalyptic number.

It is an amenable number.

21706381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21706381 is an equidigital number, since it uses as much as digits as its factorization.

21706381 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 21706381 is about 4659.0107319044. The cubic root of 21706381 is about 278.9517822832.

The spelling of 21706381 in words is "twenty-one million, seven hundred six thousand, three hundred eighty-one".