21900031 has 2 divisors, whose sum is σ = 21900032. Its totient is φ = 21900030.

The previous prime is 21900019. The next prime is 21900049. The reversal of 21900031 is 13000912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21900031 - 2¹⁹ = 21375743 is a prime.

It is a super-2 number, since 2×21900031² = 959222715601922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21899978 and 21900014.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21900091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10950015 + 10950016.

It is an arithmetic number, because the mean of its divisors is an integer number (10950016).

Almost surely, 2^21900031 is an apocalyptic number.

21900031 is a deficient number, since it is larger than the sum of its proper divisors (1).

21900031 is an equidigital number, since it uses as much as digits as its factorization.

21900031 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 54, while the sum is 16.

The square root of 21900031 is about 4679.7468948651. The cubic root of 21900031 is about 279.7788687740.

Adding to 21900031 its reverse (13000912), we get a palindrome (34900943).

The spelling of 21900031 in words is "twenty-one million, nine hundred thousand, thirty-one".