1666421 has 2 divisors, whose sum is σ = 1666422. Its totient is φ = 1666420.

The previous prime is 1666417. The next prime is 1666429. The reversal of 1666421 is 1246661.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1661521 + 4900 = 1289^2 + 70^2 .

It is a cyclic number.

It is not a de Polignac number, because 1666421 - 2² = 1666417 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1666429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833210 + 833211.

It is an arithmetic number, because the mean of its divisors is an integer number (833211).

2^1666421 is an apocalyptic number.

It is an amenable number.

1666421 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666421 is an equidigital number, since it uses as much as digits as its factorization.

1666421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728, while the sum is 26.

The square root of 1666421 is about 1290.8992989385. The cubic root of 1666421 is about 118.5572844626.

The spelling of 1666421 in words is "one million, six hundred sixty-six thousand, four hundred twenty-one".