21931031 has 2 divisors, whose sum is σ = 21931032. Its totient is φ = 21931030.

The previous prime is 21931027. The next prime is 21931033. The reversal of 21931031 is 13013912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21931031 - 2² = 21931027 is a prime.

It is a super-2 number, since 2×21931031² = 961940241445922, which contains 22 as substring.

Together with 21931033, 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 = 21930994 and 21931012.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21931033) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965515 + 10965516.

It is an arithmetic number, because the mean of its divisors is an integer number (10965516).

Almost surely, 2^21931031 is an apocalyptic number.

21931031 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931031 is an equidigital number, since it uses as much as digits as its factorization.

21931031 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 162, while the sum is 20.

The square root of 21931031 is about 4683.0578685299. The cubic root of 21931031 is about 279.9108176861.

Adding to 21931031 its reverse (13013912), we get a palindrome (34944943).

The spelling of 21931031 in words is "twenty-one million, nine hundred thirty-one thousand, thirty-one".