1663721 has 2 divisors, whose sum is σ = 1663722. Its totient is φ = 1663720.

The previous prime is 1663709. The next prime is 1663747. The reversal of 1663721 is 1273661.

It is an a-pointer prime, because the next prime (1663747) can be obtained adding 1663721 to its sum of digits (26).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1413721 + 250000 = 1189^2 + 500^2 .

It is a cyclic number.

It is not a de Polignac number, because 1663721 - 2¹⁰ = 1662697 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (1663771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 831860 + 831861.

It is an arithmetic number, because the mean of its divisors is an integer number (831861).

2^1663721 is an apocalyptic number.

It is an amenable number.

1663721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1663721 is an equidigital number, since it uses as much as digits as its factorization.

1663721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1512, while the sum is 26.

The square root of 1663721 is about 1289.8530924101. The cubic root of 1663721 is about 118.4932194783.

The spelling of 1663721 in words is "one million, six hundred sixty-three thousand, seven hundred twenty-one".