221021261 has 2 divisors, whose sum is σ = 221021262. Its totient is φ = 221021260.

The previous prime is 221021249. The next prime is 221021263. The reversal of 221021261 is 162120122.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 183738025 + 37283236 = 13555^2 + 6106^2 .

It is a cyclic number.

It is not a de Polignac number, because 221021261 - 2⁶ = 221021197 is a prime.

It is a super-4 number, since 4×221021261⁴ (a number of 34 digits) contains 4444 as substring.

Together with 221021263, 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 (221021263) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110510630 + 110510631.

It is an arithmetic number, because the mean of its divisors is an integer number (110510631).

Almost surely, 2^221021261 is an apocalyptic number.

It is an amenable number.

221021261 is a deficient number, since it is larger than the sum of its proper divisors (1).

221021261 is an equidigital number, since it uses as much as digits as its factorization.

221021261 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 221021261 is about 14866.7838149346. The cubic root of 221021261 is about 604.6137470349.

Adding to 221021261 its reverse (162120122), we get a palindrome (383141383).

The spelling of 221021261 in words is "two hundred twenty-one million, twenty-one thousand, two hundred sixty-one".