1221666665 has 16 divisors (see below), whose sum is σ = 1571892480. Its totient is φ = 908194560.

The previous prime is 1221666653. The next prime is 1221666671. The reversal of 1221666665 is 5666661221.

It is not a de Polignac number, because 1221666665 - 2⁶ = 1221666601 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 84251 + ... + 97680.

It is an arithmetic number, because the mean of its divisors is an integer number (98243280).

Almost surely, 2^1221666665 is an apocalyptic number.

It is an amenable number.

1221666665 is a deficient number, since it is larger than the sum of its proper divisors (350225815).

1221666665 is a wasteful number, since it uses less digits than its factorization.

1221666665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 182032.

The product of its digits is 155520, while the sum is 41.

The square root of 1221666665 is about 34952.3484904806. The cubic root of 1221666665 is about 1069.0160882780.

The spelling of 1221666665 in words is "one billion, two hundred twenty-one million, six hundred sixty-six thousand, six hundred sixty-five".