21098261 has 2 divisors, whose sum is σ = 21098262. Its totient is φ = 21098260.

The previous prime is 21098257. The next prime is 21098263. The reversal of 21098261 is 16289012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11519236 + 9579025 = 3394^2 + 3095^2 .

It is a cyclic number.

It is not a de Polignac number, because 21098261 - 2² = 21098257 is a prime.

It is a Sophie Germain prime.

Together with 21098263, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is equal to p_1335773 and since 21098261 and 1335773 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21098263) 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, 10549130 + 10549131.

It is an arithmetic number, because the mean of its divisors is an integer number (10549131).

Almost surely, 2^21098261 is an apocalyptic number.

It is an amenable number.

21098261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21098261 is an equidigital number, since it uses as much as digits as its factorization.

21098261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1728, while the sum is 29.

The square root of 21098261 is about 4593.2843369424. The cubic root of 21098261 is about 276.3220571910.

Subtracting from 21098261 its reverse (16289012), we obtain a square (4809249 = 2193²).

The spelling of 21098261 in words is "twenty-one million, ninety-eight thousand, two hundred sixty-one".