1221535553 has 12 divisors (see below), whose sum is σ = 1444268052. Its totient is φ = 1029863520.

The previous prime is 1221535547. The next prime is 1221535577. The reversal of 1221535553 is 3555351221.

It can be written as a sum of positive squares in 2 ways, for example, as 146482609 + 1075052944 = 12103^2 + 32788^2 .

It is not a de Polignac number, because 1221535553 - 2¹⁶ = 1221470017 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1221535583) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 201350 + ... + 207327.

It is an arithmetic number, because the mean of its divisors is an integer number (120355671).

Almost surely, 2^1221535553 is an apocalyptic number.

It is an amenable number.

1221535553 is a deficient number, since it is larger than the sum of its proper divisors (222732499).

1221535553 is an equidigital number, since it uses as much as digits as its factorization.

1221535553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 408752 (or 408745 counting only the distinct ones).

The product of its digits is 22500, while the sum is 32.

The square root of 1221535553 is about 34950.4728580315. The cubic root of 1221535553 is about 1068.9778438436.

Adding to 1221535553 its reverse (3555351221), we get a palindrome (4776886774).

The spelling of 1221535553 in words is "one billion, two hundred twenty-one million, five hundred thirty-five thousand, five hundred fifty-three".