21931001 has 2 divisors, whose sum is σ = 21931002. Its totient is φ = 21931000.

The previous prime is 21930991. The next prime is 21931027. The reversal of 21931001 is 10013912.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20241001 + 1690000 = 4499^2 + 1300^2 .

It is a cyclic number.

It is not a de Polignac number, because 21931001 - 2¹⁰ = 21929977 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21931031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965500 + 10965501.

It is an arithmetic number, because the mean of its divisors is an integer number (10965501).

Almost surely, 2^21931001 is an apocalyptic number.

It is an amenable number.

21931001 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931001 is an equidigital number, since it uses as much as digits as its factorization.

21931001 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 54, while the sum is 17.

The square root of 21931001 is about 4683.0546654935. The cubic root of 21931001 is about 279.9106900538.

Adding to 21931001 its reverse (10013912), we get a palindrome (31944913).

The spelling of 21931001 in words is "twenty-one million, nine hundred thirty-one thousand, one".