21810197 has 2 divisors, whose sum is σ = 21810198. Its totient is φ = 21810196.

The previous prime is 21810179. The next prime is 21810199. The reversal of 21810197 is 79101812.

Together with previous prime (21810179) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15689521 + 6120676 = 3961^2 + 2474^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21810197 is a prime.

Together with 21810199, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21810199) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10905098 + 10905099.

It is an arithmetic number, because the mean of its divisors is an integer number (10905099).

Almost surely, 2^21810197 is an apocalyptic number.

It is an amenable number.

21810197 is a deficient number, since it is larger than the sum of its proper divisors (1).

21810197 is an equidigital number, since it uses as much as digits as its factorization.

21810197 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1008, while the sum is 29.

The square root of 21810197 is about 4670.1388630318. The cubic root of 21810197 is about 279.3957932197.

The spelling of 21810197 in words is "twenty-one million, eight hundred ten thousand, one hundred ninety-seven".