1221021543 has 24 divisors (see below), whose sum is σ = 1895317488. Its totient is φ = 697178496.

The previous prime is 1221021523. The next prime is 1221021587. The reversal of 1221021543 is 3451201221.

It is not a de Polignac number, because 1221021543 - 2⁵ = 1221021511 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221021523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 252355 + ... + 257147.

It is an arithmetic number, because the mean of its divisors is an integer number (78971562).

Almost surely, 2^1221021543 is an apocalyptic number.

1221021543 is a deficient number, since it is larger than the sum of its proper divisors (674295945).

1221021543 is a wasteful number, since it uses less digits than its factorization.

1221021543 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6543 (or 6536 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 1221021543 is about 34943.1186787900. The cubic root of 1221021543 is about 1068.8278843963.

Adding to 1221021543 its reverse (3451201221), we get a palindrome (4672222764).

The spelling of 1221021543 in words is "one billion, two hundred twenty-one million, twenty-one thousand, five hundred forty-three".