21055261 has 2 divisors, whose sum is σ = 21055262. Its totient is φ = 21055260.

The previous prime is 21055259. The next prime is 21055277. The reversal of 21055261 is 16255012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20520900 + 534361 = 4530^2 + 731^2 .

It is a cyclic number.

It is not a de Polignac number, because 21055261 - 2¹ = 21055259 is a prime.

Together with 21055259, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21055291) 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, 10527630 + 10527631.

It is an arithmetic number, because the mean of its divisors is an integer number (10527631).

Almost surely, 2^21055261 is an apocalyptic number.

It is an amenable number.

21055261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21055261 is an equidigital number, since it uses as much as digits as its factorization.

21055261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 600, while the sum is 22.

The square root of 21055261 is about 4588.6012029811. The cubic root of 21055261 is about 276.1342071169.

It can be divided in two parts, 21055 and 261, that added together give a square (21316 = 146²).

The spelling of 21055261 in words is "twenty-one million, fifty-five thousand, two hundred sixty-one".