1668721 has 2 divisors, whose sum is σ = 1668722. Its totient is φ = 1668720.

The previous prime is 1668683. The next prime is 1668727. The reversal of 1668721 is 1278661.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1290496 + 378225 = 1136^2 + 615^2 .

It is a cyclic number.

It is not a de Polignac number, because 1668721 - 2⁷ = 1668593 is a prime.

It is a nialpdrome in base 6.

It is not a weakly prime, because it can be changed into another prime (1668727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 834360 + 834361.

It is an arithmetic number, because the mean of its divisors is an integer number (834361).

2^1668721 is an apocalyptic number.

It is an amenable number.

1668721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1668721 is an equidigital number, since it uses as much as digits as its factorization.

1668721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4032, while the sum is 31.

The square root of 1668721 is about 1291.7898435891. The cubic root of 1668721 is about 118.6118037784.

The spelling of 1668721 in words is "one million, six hundred sixty-eight thousand, seven hundred twenty-one".