21090197 has 2 divisors, whose sum is σ = 21090198. Its totient is φ = 21090196.

The previous prime is 21090161. The next prime is 21090227. The reversal of 21090197 is 79109012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11566801 + 9523396 = 3401^2 + 3086^2 .

It is a cyclic number.

It is not a de Polignac number, because 21090197 - 2¹⁸ = 20828053 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21090107) 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, 10545098 + 10545099.

It is an arithmetic number, because the mean of its divisors is an integer number (10545099).

Almost surely, 2^21090197 is an apocalyptic number.

It is an amenable number.

21090197 is a deficient number, since it is larger than the sum of its proper divisors (1).

21090197 is an equidigital number, since it uses as much as digits as its factorization.

21090197 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1134, while the sum is 29.

The square root of 21090197 is about 4592.4064497821. The cubic root of 21090197 is about 276.2868482067.

The spelling of 21090197 in words is "twenty-one million, ninety thousand, one hundred ninety-seven".