21931237 has 2 divisors, whose sum is σ = 21931238. Its totient is φ = 21931236.

The previous prime is 21931223. The next prime is 21931243. The reversal of 21931237 is 73213912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12967201 + 8964036 = 3601^2 + 2994^2 .

It is a cyclic number.

It is not a de Polignac number, because 21931237 - 2⁷ = 21931109 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21931297) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965618 + 10965619.

It is an arithmetic number, because the mean of its divisors is an integer number (10965619).

Almost surely, 2^21931237 is an apocalyptic number.

It is an amenable number.

21931237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931237 is an equidigital number, since it uses as much as digits as its factorization.

21931237 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2268, while the sum is 28.

The square root of 21931237 is about 4683.0798626545. The cubic root of 21931237 is about 279.9116940919.

The spelling of 21931237 in words is "twenty-one million, nine hundred thirty-one thousand, two hundred thirty-seven".