21706031 has 2 divisors, whose sum is σ = 21706032. Its totient is φ = 21706030.

The previous prime is 21706021. The next prime is 21706033. The reversal of 21706031 is 13060712.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21706031 - 2¹⁰ = 21705007 is a prime.

It is a super-2 number, since 2×21706031² = 942303563545922, which contains 22 as substring.

Together with 21706033, 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 = 21705994 and 21706012.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21706033) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10853015 + 10853016.

It is an arithmetic number, because the mean of its divisors is an integer number (10853016).

Almost surely, 2^21706031 is an apocalyptic number.

21706031 is a deficient number, since it is larger than the sum of its proper divisors (1).

21706031 is an equidigital number, since it uses as much as digits as its factorization.

21706031 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 252, while the sum is 20.

The square root of 21706031 is about 4658.9731701309. The cubic root of 21706031 is about 278.9502829753.

Adding to 21706031 its reverse (13060712), we get a palindrome (34766743).

The spelling of 21706031 in words is "twenty-one million, seven hundred six thousand, thirty-one".