21000000031 has 2 divisors, whose sum is σ = 21000000032. Its totient is φ = 21000000030.

The previous prime is 21000000029. The next prime is 21000000041. The reversal of 21000000031 is 13000000012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21000000031 - 2¹ = 21000000029 is a prime.

It is a super-2 number, since 2×21000000031² (a number of 21 digits) contains 22 as substring.

Together with 21000000029, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 20999999960 and 21000000023.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21000000041) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500000015 + 10500000016.

It is an arithmetic number, because the mean of its divisors is an integer number (10500000016).

Almost surely, 2^21000000031 is an apocalyptic number.

21000000031 is a deficient number, since it is larger than the sum of its proper divisors (1).

21000000031 is an equidigital number, since it uses as much as digits as its factorization.

21000000031 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6, while the sum is 7.

Adding to 21000000031 its reverse (13000000012), we get a palindrome (34000000043).

The spelling of 21000000031 in words is "twenty-one billion, thirty-one", and thus it is an aban number and an uban number.