1663561 has 4 divisors (see below), whose sum is σ = 1670292. Its totient is φ = 1656832.

The previous prime is 1663549. The next prime is 1663579. The reversal of 1663561 is 1653661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1653661 = 71 ⋅23291.

It can be written as a sum of positive squares in 2 ways, for example, as 1092025 + 571536 = 1045^2 + 756^2 .

It is a cyclic number.

It is not a de Polignac number, because 1663561 - 2¹⁹ = 1139273 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1663861) 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, 2980 + ... + 3493.

It is an arithmetic number, because the mean of its divisors is an integer number (417573).

2^1663561 is an apocalyptic number.

It is an amenable number.

1663561 is a deficient number, since it is larger than the sum of its proper divisors (6731).

1663561 is an equidigital number, since it uses as much as digits as its factorization.

1663561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6730.

The product of its digits is 3240, while the sum is 28.

The square root of 1663561 is about 1289.7910683518. The cubic root of 1663561 is about 118.4894208600.

The spelling of 1663561 in words is "one million, six hundred sixty-three thousand, five hundred sixty-one".