1221220021 has 4 divisors (see below), whose sum is σ = 1395680032. Its totient is φ = 1046760012.

The previous prime is 1221220001. The next prime is 1221220027. The reversal of 1221220021 is 1200221221.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1200221221 = 1217 ⋅986213.

It is a cyclic number.

It is not a de Polignac number, because 1221220021 - 2¹⁷ = 1221088949 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1221219983 and 1221220010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221220027) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 87229995 + ... + 87230008.

It is an arithmetic number, because the mean of its divisors is an integer number (348920008).

Almost surely, 2^1221220021 is an apocalyptic number.

It is an amenable number.

1221220021 is a deficient number, since it is larger than the sum of its proper divisors (174460011).

1221220021 is an equidigital number, since it uses as much as digits as its factorization.

1221220021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 174460010.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 1221220021 is about 34945.9585789258. The cubic root of 1221220021 is about 1068.8857941928.

Adding to 1221220021 its reverse (1200221221), we get a palindrome (2421441242).

The spelling of 1221220021 in words is "one billion, two hundred twenty-one million, two hundred twenty thousand, twenty-one".