1221543665 has 8 divisors (see below), whose sum is σ = 1487731200. Its totient is φ = 962649072.

The previous prime is 1221543637. The next prime is 1221543667. The reversal of 1221543665 is 5663451221.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1221543665 - 2²⁴ = 1204766449 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1221543667) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1822865 + ... + 1823534.

It is an arithmetic number, because the mean of its divisors is an integer number (185966400).

Almost surely, 2^1221543665 is an apocalyptic number.

It is an amenable number.

1221543665 is a deficient number, since it is larger than the sum of its proper divisors (266187535).

1221543665 is an equidigital number, since it uses as much as digits as its factorization.

1221543665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3646471.

The product of its digits is 43200, while the sum is 35.

The square root of 1221543665 is about 34950.5889077709. The cubic root of 1221543665 is about 1068.9802101355.

Adding to 1221543665 its reverse (5663451221), we get a palindrome (6884994886).

The spelling of 1221543665 in words is "one billion, two hundred twenty-one million, five hundred forty-three thousand, six hundred sixty-five".