1221665 has 4 divisors (see below), whose sum is σ = 1466004. Its totient is φ = 977328.

The previous prime is 1221659. The next prime is 1221667. The reversal of 1221665 is 5661221.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 595984 + 625681 = 772^2 + 791^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221665 - 2⁶ = 1221601 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1221665.

It is not an unprimeable number, because it can be changed into a prime (1221667) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 122162 + ... + 122171.

It is an arithmetic number, because the mean of its divisors is an integer number (366501).

2^1221665 is an apocalyptic number.

It is an amenable number.

1221665 is a deficient number, since it is larger than the sum of its proper divisors (244339).

1221665 is an equidigital number, since it uses as much as digits as its factorization.

1221665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 244338.

The product of its digits is 720, while the sum is 23.

The square root of 1221665 is about 1105.2895548226. The cubic root of 1221665 is about 106.9015602627.

Adding to 1221665 its reverse (5661221), we get a palindrome (6882886).

The spelling of 1221665 in words is "one million, two hundred twenty-one thousand, six hundred sixty-five".