1661651 has 4 divisors (see below), whose sum is σ = 1665600. Its totient is φ = 1657704.

The previous prime is 1661641. The next prime is 1661659. The reversal of 1661651 is 1561661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1561661 = 61 ⋅25601.

It is a cyclic number.

It is not a de Polignac number, because 1661651 - 2⁶ = 1661587 is a prime.

It is a super-2 number, since 2×1661651² = 5522168091602, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1661651.

It is not an unprimeable number, because it can be changed into a prime (1661659) 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, 1256 + ... + 2213.

It is an arithmetic number, because the mean of its divisors is an integer number (416400).

2^1661651 is an apocalyptic number.

1661651 is a deficient number, since it is larger than the sum of its proper divisors (3949).

1661651 is an equidigital number, since it uses as much as digits as its factorization.

1661651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3948.

The product of its digits is 1080, while the sum is 26.

The square root of 1661651 is about 1289.0504257010. The cubic root of 1661651 is about 118.4440560346. Note that the first 3 decimals are identical.

The spelling of 1661651 in words is "one million, six hundred sixty-one thousand, six hundred fifty-one".