221221421 has 2 divisors, whose sum is σ = 221221422. Its totient is φ = 221221420.

The previous prime is 221221397. The next prime is 221221423. The reversal of 221221421 is 124122122.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 220849321 + 372100 = 14861^2 + 610^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-221221421 is a prime.

Together with 221221423, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 221221421.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (221221423) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 110610710 + 110610711.

It is an arithmetic number, because the mean of its divisors is an integer number (110610711).

Almost surely, 2^221221421 is an apocalyptic number.

It is an amenable number.

221221421 is a deficient number, since it is larger than the sum of its proper divisors (1).

221221421 is an equidigital number, since it uses as much as digits as its factorization.

221221421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 128, while the sum is 17.

The square root of 221221421 is about 14873.5140770431. The cubic root of 221221421 is about 604.7962075715.

Adding to 221221421 its reverse (124122122), we get a palindrome (345343543).

The spelling of 221221421 in words is "two hundred twenty-one million, two hundred twenty-one thousand, four hundred twenty-one".