1221200021 has 2 divisors, whose sum is σ = 1221200022. Its totient is φ = 1221200020.

The previous prime is 1221200017. The next prime is 1221200023. The reversal of 1221200021 is 1200021221.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 855855025 + 365344996 = 29255^2 + 19114^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221200021 - 2² = 1221200017 is a prime.

Together with 1221200023, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 1221199975 and 1221200011.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221200023) 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, 610600010 + 610600011.

It is an arithmetic number, because the mean of its divisors is an integer number (610600011).

Almost surely, 2^1221200021 is an apocalyptic number.

It is an amenable number.

1221200021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221200021 is an equidigital number, since it uses as much as digits as its factorization.

1221200021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 1221200021 is about 34945.6724216318. The cubic root of 1221200021 is about 1068.8799590901.

Adding to 1221200021 its reverse (1200021221), we get a palindrome (2421221242).

The spelling of 1221200021 in words is "one billion, two hundred twenty-one million, two hundred thousand, twenty-one".