21706931 has 2 divisors, whose sum is σ = 21706932. Its totient is φ = 21706930.

The previous prime is 21706921. The next prime is 21706933. The reversal of 21706931 is 13960712.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21706931 is a prime.

It is a super-2 number, since 2×21706931² = 942381706877522, which contains 22 as substring.

Together with 21706933, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21706894 and 21706903.

It is not a weakly prime, because it can be changed into another prime (21706933) 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, 10853465 + 10853466.

It is an arithmetic number, because the mean of its divisors is an integer number (10853466).

Almost surely, 2^21706931 is an apocalyptic number.

21706931 is a deficient number, since it is larger than the sum of its proper divisors (1).

21706931 is an equidigital number, since it uses as much as digits as its factorization.

21706931 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2268, while the sum is 29.

The square root of 21706931 is about 4659.0697569365. The cubic root of 21706931 is about 278.9541383060.

The spelling of 21706931 in words is "twenty-one million, seven hundred six thousand, nine hundred thirty-one".