21220261 has 2 divisors, whose sum is σ = 21220262. Its totient is φ = 21220260.

The previous prime is 21220231. The next prime is 21220313. The reversal of 21220261 is 16202212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11492100 + 9728161 = 3390^2 + 3119^2 .

It is a cyclic number.

It is not a de Polignac number, because 21220261 - 2⁹ = 21219749 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21220211) 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, 10610130 + 10610131.

It is an arithmetic number, because the mean of its divisors is an integer number (10610131).

Almost surely, 2^21220261 is an apocalyptic number.

It is an amenable number.

21220261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21220261 is an equidigital number, since it uses as much as digits as its factorization.

21220261 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 96, while the sum is 16.

The square root of 21220261 is about 4606.5454518544. The cubic root of 21220261 is about 276.8536416152.

Adding to 21220261 its reverse (16202212), we get a palindrome (37422473).

The spelling of 21220261 in words is "twenty-one million, two hundred twenty thousand, two hundred sixty-one".