1661621 has 4 divisors (see below), whose sum is σ = 1789452. Its totient is φ = 1533792.

The previous prime is 1661599. The next prime is 1661623. The reversal of 1661621 is 1261661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1261661 = 131 ⋅9631.

It can be written as a sum of positive squares in 2 ways, for example, as 255025 + 1406596 = 505^2 + 1186^2 .

It is not a de Polignac number, because 1661621 - 2⁶ = 1661557 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661623) 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, 63896 + ... + 63921.

It is an arithmetic number, because the mean of its divisors is an integer number (447363).

2^1661621 is an apocalyptic number.

It is an amenable number.

1661621 is a deficient number, since it is larger than the sum of its proper divisors (127831).

1661621 is a wasteful number, since it uses less digits than its factorization.

1661621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 127830.

The product of its digits is 432, while the sum is 23.

The square root of 1661621 is about 1289.0387891759. The cubic root of 1661621 is about 118.4433432209.

The spelling of 1661621 in words is "one million, six hundred sixty-one thousand, six hundred twenty-one".