1221686857 has 4 divisors (see below), whose sum is σ = 1263814020. Its totient is φ = 1179559696.

The previous prime is 1221686821. The next prime is 1221686887. The reversal of 1221686857 is 7586861221.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 7586861221 = 307 ⋅24712903.

It can be written as a sum of positive squares in 2 ways, for example, as 191020041 + 1030666816 = 13821^2 + 32104^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1221686857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1221686887) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21063538 + ... + 21063595.

It is an arithmetic number, because the mean of its divisors is an integer number (315953505).

Almost surely, 2^1221686857 is an apocalyptic number.

It is an amenable number.

1221686857 is a deficient number, since it is larger than the sum of its proper divisors (42127163).

1221686857 is an equidigital number, since it uses as much as digits as its factorization.

1221686857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42127162.

The product of its digits is 322560, while the sum is 46.

The square root of 1221686857 is about 34952.6373396916. The cubic root of 1221686857 is about 1069.0219778971.

The spelling of 1221686857 in words is "one billion, two hundred twenty-one million, six hundred eighty-six thousand, eight hundred fifty-seven".