1221155021 has 2 divisors, whose sum is σ = 1221155022. Its totient is φ = 1221155020.

The previous prime is 1221155017. The next prime is 1221155041. The reversal of 1221155021 is 1205511221.

It is an a-pointer prime, because the next prime (1221155041) can be obtained adding 1221155021 to its sum of digits (20).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 954192100 + 266962921 = 30890^2 + 16339^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221155021 - 2² = 1221155017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 1221154984 and 1221155002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221155011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610577510 + 610577511.

It is an arithmetic number, because the mean of its divisors is an integer number (610577511).

Almost surely, 2^1221155021 is an apocalyptic number.

It is an amenable number.

1221155021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221155021 is an equidigital number, since it uses as much as digits as its factorization.

1221155021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 200, while the sum is 20.

The square root of 1221155021 is about 34945.0285591527. The cubic root of 1221155021 is about 1068.8668298762.

Adding to 1221155021 its reverse (1205511221), we get a palindrome (2426666242).

The spelling of 1221155021 in words is "one billion, two hundred twenty-one million, one hundred fifty-five thousand, twenty-one".